Policy on Listeria monocytogenes  
in Ready-to-Eat Foods 
 
   
 
Bureau of Microbial Hazards 
nd Food Branch 
ntification Number:  FD-FSNP 0071 
0. 
:                   
 
 
    Food Directorate 
Health Products a
 
 
 
Ide
       
 Issue Date:     November 3, 201
Effective Date      April 1, 2011. 
 
 
 
 
 
  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   2 
 Table of Contents 
 
1      Summary ............................................................................................................................... ...............3 
 
2 Purpose and Scope .............................................................................................................................4 
 
3 Roles and Responsibilities .................................................................................................................4 
3.1 Industry ............................................................................................................................... .......4 
3.2 Government ............................................................................................................................... .5 
3.3 Consumers ............................................................................................................................... ...5 
 
4 Background ............................................................................................................................... ..........6 
 
5 Scientific Basis for Listeria monocytogene s Criteria in Ready-to-Eat Foods ................................7 
 
6 Compliance Criteria for the Control of Listeria monocytogenes  in Ready-to-Eat Foods .............8 
6.1    Assignment of Risk Classification of Read y-to-Eat Foods According to Consumer Risk .....8 
6.2    Applying the Criteria to Domestic, Imported and Exported Ready-to-Eat Foods ................10 
6.2.1.  Domestic facilities: ..........................................................................................................10 
6.2.1.1.  Environmental control: .........................................................................................10 
6.2.1.2.  Product control: .....................................................................................................11 
6.2.2.  Imported RTE products: ................................................................................................11 
6.2.3.  Exported RTE products: ................................................................................................12 
 
7    Achieving Compliance with the Criteria for Ready-to-Eat Foods .................................................12 
7.1 Requirements for the Manufacture of Ready-to-Eat Food Products .................................12 
7.2 Environmental Sampling (Figures 1, 2 and 3) ......................................................................13 
7.3 Sampling and Analysis of Finished Ready-to-Eat Foods .....................................................20 
7.3 Sampling and Analysis of Finished Ready-to-Eat Foods .....................................................21 
7.4 Importance of Trend Analysis and Quality Assurance Tools ..............................................26 
 
8 Development of Educational Materials for Cons umers and Others Involved in  Food Handling 
and Preparation ............................................................................................................................... .........26 
8.1 Contributions of Health Canada Scient ists to Published Information Related to ....................26 
Foodborne Listeriosis ...........................................................................................................................26 
 
Appendix A: Definitions ...........................................................................................................................28 
 
Appendix B: Major Reported Foodborne Listeriosis Outbreaks: ........................................................34 
 
Appendix C: Use of Food Additives, Processing Ai ds and/or Post-Lethality Treatments for Ready-
to-Eat Foods............................................................................................................................... ................38 
 
Appendix D: Isolation of Listeria moncytogenes in Foods .....................................................................40 
 
Appendix E: Enumeration of Listeria monocytogenes  in Foods ............................................................56 
 
References ............................................................................................................................... ...................63   
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   3 
                                                 1          Summary 
 
The Canadian “Policy on Listeria monocytogenes in ready-to-eat foods” (h ereafter referred to as 
the Listeria policy) is based on Good Manufacturing Practices1 (GMPs) and the principles of 
HACCP (Hazard Analysis Critical Control Point; see Appendix A).  This policy was developed 
using a health risk assessment (HRA) approach  and uses as its foundation a combination of 
inspection, environmental sampling2 and end-product testing to verify control of Listeria 
monocytogenes in ready-to-eat (RTE) foods (RTE food is defined in Appendix A). Focus is 
given to environmental verification and control, es pecially in post-lethality areas, as applicable.  
This policy applies to RTE food sold in Canada , produced both domestically and imported.  The 
present policy revises and replaces the Policy on Listeria monocytogenes in ready-to-eat foods 
dated October 4, 2004.  
 
The current policy differs from the 2004 document in the following:   1) New end-product compliance criteria have been developed. These are similar to the 
International Codex Alimentarius Co mmission standards (CAC, 2009a).   
2) The definitions of RTE foods in which growth of L. monocytogenes can or cannot occur 
have been modified and/or developed.  Valid ation data to support the categorization of 
RTE foods (i.e., Category 2A or 2B) are to be reviewed by regulatory authorities.  The list of food products implicated in list eriosis outbreaks has been updated.   
3) The compliance action decision tree, including environmental testing for Listeria  spp.
3  
and end-product testing for L. monocytogenes , has been modified to include more details 
related to sampling.  
4) It now states that an environmental monitoring program should be included in all plants 
used in the production of RTE foods , as defined in this policy.   
5) It encourages the use of pos t-lethality treatments and/or L. monocytogenes growth 
inhibitors.   
6) There is an increased focus on outreach with  the federal/provincial/territorial community 
to increase awareness of the risks of foodborne  listeriosis and to provide guidance on how 
to reduce the risks of acquiri ng listeriosis to personnel in institutions where high-risk 
people may be exposed.  
 In this policy, RTE foods have been classified into two categor ies, based upon health risk.  
Category 1 contains products in which the growth of L. monocytogenes can occur (see Appendix 
A).  These should receive the highest priority fo r industry verification a nd control, as well as 
regulatory oversight and compliance activities.  The presence of L. monocytogenes in these 
Category 1 RTE foods will likely trigger a Health Risk 1 concer n (Health Risk Categories are 
 
1 The term GMPs in the text is used as a generic term and includes all key conditions and control 
measures necessary for processors to ensure the safet y and the suitability of food during manufacturing. 
2 For the purposes of this document, this includes both food contact and non-food contact surfaces. 
 3 For the purposes of this  document, this includes L. monocytogenes .  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   4 
 defined in Appendix A).  Category 2 contains two subgroups: 2A) RTE food products in which 
limited growth of L. monocytogenes  to levels not greater than 100 CFU/g can occur throughout 
the stated shelf-life (e.g., durable  life date shown as a “best before” date on the package); and 
2B) RTE food products in which the growth of L. monocytogenes cannot occur th roughout the 
expected shelf life of that food (see Appendix A).  These products should receive a lower priority 
with regards to industry verifica tion and control, as well as re gulatory oversight and compliance 
activities.   
 This revised policy should lead to an enha ncement of the verification and control of Listeria  spp. 
in the food processing environment, permit earlier identification of a ny potential persistent 
contamination of the plant environment and provide an increased ability to identify and mitigate against L. monocytogenes  contamination of finished product.  These actions will provide an early 
warning and permit the appropriate in terventions to protect consumers.  
  
2 Purpose and Scope  
 
The goal of this policy is to prot ect the health of Canadian cons umers and to provide guidance to 
industry and regulatory authorities rega rding the verification and control of L. monocytogenes in 
RTE foods.  It also provides guidance to re gulatory author ities regarding oversight and 
compliance activities of RTE foods contaminated with L. monocytogenes .  Consistent with the 
current knowledge that the risk of listeriosis is increased in RTE foods which support the growth 
of L. monocytogenes and which have extended shelf-lives, higher priority is  placed on RTE 
foods in which the growth of L. monocytogenes can occur.  In addition to providing guidance to 
other food safety regulators (e.g., the Canadian F ood Inspection Agency and provincial/territorial 
governments) and decision-makers, this policy ca n also guide RTE food processors in their 
verification activities with respect to the presence of L. monocytogenes  in both the plant 
environment and the finished product.  In additio n to what is outlined in this policy document, 
additional regulatory requirements  specific for particular food commodities may also be 
applicable (e.g., the Canadian Food Inspection Agency (CFIA)’s Meat Hygiene Directives 
(CFIA, 2009a)).  Note that the information contai ned in this policy is ba sed on the current state 
of scientific evidence and th at developments are on-going. 
 
 
3 Roles and Responsibilities  
 
This policy, developed as a joint effort between Health Canada (HC), the (CFIA) and the Public 
Health Agency of Canada (PHAC), takes into ac count the roles and responsibilities of industry, 
government and consumers.   
  
3.1 Industry 
 
It is industry’s role and res ponsibility to comply with all applicable legislative and 
regulatory requirements which incl ude Sections 4 and 7 of the Food and Drug Act  
(Government of Canada, 2010a). As  L. monocytogenes  can be found in the environment  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   5 
 of food processing plants, RTE food pr ocessors should have an effective                                                    
GMP and/or HACCP system to minimize all potential sources of food contamination. 
These should address L. monocytogenes  in the environment of pr ocessing establishments.  
In this regard, the importance of sani tation should not be overlooked.  Sanitation 
management can lead to intervention i nnovations (e.g., effective remediation) and 
sanitary design improvements (e.g., equipment a nd facility).  RTE f ood processors should 
also strongly consider introduci ng within their food safety sy stems one or more validated 
controls for the elimination of L. monocytogenes from their products (e.g., use of a post-
lethality treatment).  Furthermore, envir onmental and end-product sampling schemes and 
the use of microbiological testing as a verifi cation tool to demonstrate the efficacy of the 
control measures put in place to address L. monocytogenes  are recommended. Food 
processing plants should carry out regula r environmental sampling, as described in 
Figures 1, 2 and 3, to verify the effectivene ss of their sanitation pr ogram for controlling 
Listeria  spp.  in the plant environment, and should in crease sanitation efforts and control 
measures in areas where Listeria spp. are found. 
 
 
3.2 Government 
 
Health Canada develops food safety standard s and policies to help minimize the risk of 
foodborne illnesses. Health Canada consults  with the CFIA and provincial/territorial 
governments on the above.  Furthermore, Heal th Canada’s policies can serve as a basis 
for the development of their own internal docum entation.  It is the ro le of the CFIA and 
provincial/territorial gov ernments to oversee the food industr y to ensure that it meets its 
food safety responsibilities (Health Canada, 2010 a).  The role of the PHAC is to promote 
and protect the health of Canadians thr ough leadership, partnership, innovation and 
action in public health (PHAC, 2007).  The PHAC, the CFIA and Health Canada work 
together with public health officials and provi ncial/territorial ministries of health to 
investigate the source of any L. monocytogenes related illnesses when an outbreak is 
suspected.  PHAC has already begun to play  a more active role in food surveillance 
across the country, e.g., C-EnterNet, a multi-pa rtner program designed to detect changes 
in trends in human enteric disease and in levels of pathogen exposure from food, animal 
and water sources in Canada (PHAC, 2009a).   In addition, the three federal departments 
provide reference laboratory services, conduc t food safety investigations, HRAs and 
recall actions.   
 It is also the role of the government of Canada to brie f the medical community, public 
health officials, the food industry an d consumers on many issues related to L. 
monocytogenes and listeriosis.   
  
3.3 Consumers 
 
In addition to government agencies and food industries working diligently to minimize 
the exposure to L. monocytogenes , consumers also have an impor tant role to play.  That  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   6 
 role calls for Canadians to learn and adopt safe food handling, responsible food selection 
and safe preparation practices (Health Canada, 2010a, Health Canada 2010b, Health 
Canada 2010c, Health Canada, 2010d).  Caterers and care providers for the elderly and 
other vulnerable populations have  a higher level of responsibility  in this regard.  To this 
end, Health Canada, the CFIA and the PHAC (and other provincial /territorial bodies) 
have in the past, and will continue in the fu ture, to be committed to the development and 
delivery of science-based educational material to inform consumers and care providers about the hazards associated with L. monocytogenes  in RTE food and how to minimize 
the risks of foodborne disease, with a partic ular focus on vulnerable populations and their 
families, as well as their care providers. 
 
 
4 Background 
 
L. monocytogenes  is a bacterial pathogen that is widely distributed in nature.  It has been isolated 
from faecal specimens of healthy animals and humans, as well as from sewage, silage, soil, fertilizer, vegetable matter and many foods (Far ber and Peterkin, 1991; Farber and Peterkin, 
2000; McLauchlin et al. , 2004). Important characteristics of th is organism include its ability to 
grow at temperatures of -0.4 to 45 °C, pH values of 4.4 or gr eater and water activities (a
w) of 
0.92 or higher (ICMSF, 1996).   It is estimated that up to  5 % of humans may carry L. monocytogenes  in their inte stines without 
ill effects. This organism, however, is recognized  as the causative agent of the infection known 
as listeriosis.  Listeriosis can manifest itself in two different forms, namely invasive and non-
invasive.  Invasive listeriosis  usually develops in people w ith compromised immune systems 
while non-invasive listeriosis can develop in a ny population if large numbe rs of bacteria (e.g., > 
10
3 CFU/g) are consumed.  Several modes of tr ansmission have been identified: mother-to-
foetus infection in utero or infection during ch ildbirth, infant-to-infant, animal-to-human and, 
most importantly, transmission to humans th rough consumption of contaminated food 
(McLauchlin, 1993; McLauchlin et al. , 2004) .  
 
Serious infections of L. monocytogenes  (i.e., invasive listeriosis) are manifested by septicaemia 
and/or meningoencephalitis, and may result in d eath.  The highest incidence of listeriosis is 
amongst pregnant women, the elderly (> 60 years of age) and immunocompr omised individuals.  
Among the elderly, the risk increases as individuals age, i.e., as compared to healthy individuals 
40 to 59 years of age, Canadian data show that pe rsons aged 65 to 69 years of age have a 4-times 
increased risk, while those aged 75 to 79 years of age have nearly a 9-times increased risk 
(PHAC, 2009b).  Infection of health y adults is relatively rare.  Symptoms are typically mild in 
pregnant women, however, the passage of the organism through the placenta may cause 
miscarriage, stillbirth, or perinatal septicaemia and meni ngitis in the newborn baby.  Listeria 
monocytogenes is more likely to cause death than other bacteria that cause f oodborne illness, i.e., 
20-30 % of foodborne listeriosis inf ections in high-risk individuals  may be fatal (Health Canada, 
2010a).  In addition, the potential health outcomes from listeriosis  could be serious and/or long-
lasting (Roberts et al., 2009).   
  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   7 
                                                 A number of foodborne outbreaks have been documented throughout the world (see Appendix 
B).  Listeriosis outbreaks have b een attributed to RTE food produc ts such as pâté, unacidified 
jellied pork tongue (i.e., in aspic) , rillettes, frankfurters, certai n deli-meats, chicken wrap, cheese 
made from either raw or pasteu rized milk, pasteurized milk (inc luding chocolate milk), butter, 
frozen ice cream cake, whipping cream, coleslaw , fruit salad, RTE fish products such as smoked 
mussels, gravlax (aka. gravad) and cold-smoked trout, imitation crab meat, shrimp, prepackaged 
sandwiches,  as well as rice and corn salads.   
 In Canada, the national reported rate of listeriosis  has increased over the la st several years from 
2.3 cases per million population in 2000 to 4.2 cases per million population in 2007, i.e., 2.3, 2.9, 2.9, 3.4, 3.0, 3.3, 3.9 and 4.2, respectively (PHAC, 2009c; Clark et al. , 2009).  A sharp increase 
in incidence was noted in 2008, with 7.2 cases per million population reported (PHAC, 2009b).  
This was largely attributable to two large outbreaks involving 57 and 38 confirmed cases, 
respectively (PHAC, 2009d; MSSS, 2009).  Fran ce, the United Kingdom and several other 
European countries have also re ported increases in the inciden ce of listeriosis over the last 
several years.  In these countries, the increase  has been predominantly driven by an increased 
incidence in patients > 60 years of age.  Th e reasons for this incr ease are unknown (Gillespie et 
al., 2006; Goulet et al. , 2008; ACMSF, 2009).   
  
5 Scientific Basis for Listeria monocytogene s Criteria in Ready-to-Eat Foods  
 
The foods implicated in major outbreaks of listeriosis worldwid e are typically those in which L. 
monocytogenes is present at or can grow  to levels that could presen t a risk to consumers (see 
Appendix B).  In general, the risk of acquiring foodborne listeriosis increases depending on 
factors such as host susceptib ility, the amount and frequency of consumption of a food 
contaminated with L. monocytogenes , the frequency, distribution and level of L. monocytogenes 
in the food, the potential for growth of L. monocytogenes in the food during refrigerated storage, 
the refrigerated storage temperature and/or th e duration of refrigerated storage before 
consumption (FAO/WHO, 2004a).  Therefore, the policy considers the levels of L. 
monocytogenes in a food and the potential for growth of L. monocytogenes  in a particular food.  
This is based on factors such as pH, wa ter activity, the presence of preservatives4 (see Appendix 
C) and storage conditions, e.g., temperature and shelf-life.   
 In all likelihood, Canadians cons ume foods contaminated with L. monocytogenes  on a regular 
basis; however, the incidence of  listeriosis remains relatively low.  The incidence of L. 
monocytogenes in RTE foods ranges from 0 to 10 % (Farber and Peterkin, 2000; Gombas et al. , 
2003; Ryser and Marth, 2007; Little et al. , 2009).  A large US study f ound that the prevalence of 
L. monocytogenes in RTE products such as smoked seafood, luncheon meats, salads (seafood, 
bagged precut leafy vegetable and deli) and cheeses (fresh soft, blue-veined, and mold-ripened) ranged from 0.17 to 4.7 % (Gombas et al. , 2003).  In addition, a recent UK study found that the 
 
4  A preservative acts to prolong the shelf-life of foods by protecting against deterioration caused by 
microorganisms or oxidation.  A Class II preservative is considered to be an antibacterial agent (Health 
Canada, 2007).   
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   8 
 prevalence of L. monocytogenes  in RTE products such as RTE sliced meats, hard cheeses, 
sandwiches, butter, spreadable cheese, confectionery products containing ice cream and probiotic 
drinks ranged from 0 to 7. 0 % (Little et al., 2009).   
 
A definitive dose-response model for L. monocytogenes  in humans has yet to be established.  
However, based on current case data from ar ound the world, the likelihood of any one food 
contaminated with low numbers of L. monocytogenes resulting in illness is considered to be 
remote (FAO/WHO, 2004b).  Foods containing low levels of L. monocytogenes (e.g., < 100 
CFU/g) pose very little risk (Chen et al. , 2003; FAO/WHO, 2004b).  In fact, in instances where 
foods linked to listeriosis out breaks were still available for testing, the levels of L. 
monocytogenes detected both from unopened foods and left over foods obtained from the patients 
have usually been high (i.e., >103 CFU/g), and thus these outbr eaks were due to non-compliant 
samples (European Commission Health and Consumer Protection Directorate-General, 1999).  Consequently, a lower priority should be placed on products in which the organism cannot grow 
or, has a limited potential for growth where by the levels do not exceed 100 CFU/g throughout 
the stated shelf-life (e.g., durable  life date shown as a “best before” date on the package) (see 
Table 1).    At the international level, the Codex Alimenta rius Commission and the Commission of European 
Communities have proposed similar microbiological criteria for the verification and control of L. 
monocytogenes in RTE foods, with a view towards prot ecting the health of consumers while 
ensuring fair practices in food trade (European Communities, 2007; CAC, 2009a).  The U.S. risk 
assessment, which included a risk categorizat ion of foods (FDA/FSIS, 2003), further supports 
the fact that RTE foods differ in their ability to support growth and being linked to listeriosis.   
  
6 Compliance Criteria for the Control of Listeria monocytogenes  in Ready-to-Eat 
Foods  
 
6.1       Assignment of Risk Classification of Ready-to-Eat Foods According to Consumer Risk (Categories 1 and 2: see Table 1)  
 
Category 1 RTE foods:  
 
Category 1 RTE foods are those foods which can support the growth of L. monocytogenes .  As 
presented earlier, Category 1 RTE foods  should receive the highest priority for industry 
verification and control, as we ll as regulatory oversi ght and compliance activ ities.  The presence 
of L. monocytogenes in a Category 1 food when the specifi ed sampling plan and analysis are 
applied, will be classified as a Health Risk 1, as determined in Table 1: “Sampling methodologies and compliance criteria for L. monocytogenes in RTE foods”.  A public alert and 
recall will likely be issued if the food has left the control of the proce ssor (Health Risks 1 and 2 
are defined in Appendix A).  The implicated pro duct may be considered to be in violation of 
sections 4 and 7 of the Food and Drugs Act  (Government of Canada, 2010a).  Different risk 
management actions may occur in cases where the food processor is able, as part of the safety evaluation, to present data which demonstrate that the growth of L. monocytogenes will not occur  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   9 
 in the product, for example, the validated use of preservatives, etc.  As part of the compliance 
action in such cases, arrangements for a review  and assessment to be performed by regulatory 
authorities could be made.   
  
Category 2 RTE foods: 
 
Category 2 is subdivided into: 2A) RTE food products in which limited growth of L. 
monocytogenes to levels not greater than 100 CFU/g can  occur throughout the stated shelf-life 
(e.g., durable life date shown as a “best befo re” date on the packag e); and 2B) RTE food 
products in which the growth of L. monocytogenes cannot occur throughout the expected shelf 
life of that food.   
  
Category 2A RTE foods: 
 
This category is meant to include, for example,  foods which are known to occasionally contain 
low levels of L. monocytogenes and do not have a kill step, and/or RTE refrigerated foods with a 
shelf-life of ≤ 5 days.  The latter time period would not allow sufficient time, under reasonably 
foreseeable conditions of distribution, storage and use, for L. monocytogenes  to grow to levels 
above 100 CFU/g throughout the stated shelf-life (e.g., durable life date shown as a “best before” 
date on the package).  Other foods with a sh elf-life greater than 5 days, e.g., cold-smoked 
salmon, fresh-cut produce, although they are frequen tly consumed, have not been linked to large 
documented outbreaks of listeriosis .  Notwithstanding that these f oods can support the growth of 
L. monocytogenes , the growth is generally limited because of a number of fact ors such as short 
refrigerated shelf-life, a large b ackground microflora containing anti-Listeria  lactic acid and/or 
other microorganisms, etc.  These Category 2A foods should receive a medium to low priority, 
with regards to the level of ove rsight and compliance activities.  For these foods, processors 
should validate and verify their proc esses to ensure that the levels of  L. monocytogenes are 
consistently equal to or less than 100 CFU/g duri ng the whole shelf-life of these products.  In 
general, RTE food processors should regularly monitor their products, to ensure that they 
continue to meet the criteria (e .g., limited potential for growth of L. monocytogenes to levels not 
greater than 100 CFU/g throughout th e stated shelf-life (e.g., durable  life date shown as a “best 
before” date on the package)) that justify their classification in this category.  If information is 
insufficient, inadequate or no information exists to demonstrate that there is limited growth of L. 
monocytogenes (as stated above) throughout the shelf-life , as determined by validated data, the 
food will be treated, by default, as  a RTE food in which growth of  L. monocytogenes can occur 
(i.e., Category 1).  Hence, the sampling plan and method of analysis for Category 1 foods, as 
specified in Table 1, will be a pplied.  If questions arise, it is the responsibility of the 
processor/importer to demonstrate wh at category the RTE food belongs to. 
 
 
Category 2B RTE foods: 
 
Since these foods do not support the growth of L. monocytogenes , they should receive a low 
priority, with regard to the level of oversight  and compliance activity.  In general, RTE food  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   10 
 processors would need to monitor their products to ensure that they  continue to meet the criteria 
(e.g., physico-chemical parameters such as pH and a w) that justify their classification in this 
category.  If information is insufficient, inadequate or no information exists to demonstrate that 
there is no growth of L. monocytogenes  throughout the shelf-life, as determined by validated 
data, the food will be treated, by defau lt, as a RTE food in which growth of  L. monocytogenes 
can occur (i.e., Category 1).  Hence, the sampli ng plan and method of analysis for Category 1 
foods, as specified in Table 1, will be applied.  If  questions arise, it is the responsibility of the 
processor/importer to demonstrate wh at category the RTE food belongs to. 
 Some frozen RTE foods, otherwise considered as Category 2B, may be  temperature-abused, 
causing them to thaw and thereby coul d potentially permit the growth of L. monocytogenes.   
Additionally, some Category 2 pr oducts may be intended for use in Category 1 products (e.g., 
frozen smoked fish used to make a refrigerated  smoked fish mousse) or, some RTE foods may be 
targeted for persons at high-ris k, e.g., immunocompromised, elderl y, pregnant, etc.  A finding of 
L. monocytogenes in the above foods would lead to follo w-up action(s) and he nce, an HRA may 
be required on a case-by case basis, to be c onducted by the BMH, in order to determine the 
compliance action to be taken.  These Category 2 foods may be assessed to represent a Health 
Risk 1 concern.   
RTE foods intended to be produced for High-Risk Population Groups: 
 
RTE foods that are intended to be produced for consumption by individuals who are known to be 
in the high-risk category (i.e., fi nal distribution of such RTE produc ts is known to be targeted 
specifically to pregnant women, elderly and/or immunocompromised individuals)  should receive 
the highest priority for industry verification and control, as we ll as regulatory oversight and 
compliance activities.  These RTE foods may be c onsidered to represent a Health Risk 1 and not 
Health Risk 2 concern, irrespectiv e of product type (see Table 1).  In addition, specific control 
measures may need to be taken for th ese products (e.g., in the HACCP form).   
  
6.2    Applying the Criteria to Domestic, Im ported and Exported Ready-to-Eat Foods  
 
6.2.1. Domestic facilities: 
 
6.2.1.1.  Environmental control: 
 
The relative importance of ve rifying the controls for Listeria  spp. in the processing environment 
depends on the risk to consumers if the food becomes contaminated. Inspectors of domestic 
establishments should encourage adherence to th e principles of GMP and the HACCP system.  If 
oversight reveals inadequate applic ation of GMPs that could lead to post-lethality contamination 
of a RTE food, as applicable, a review of the processor’s control program for Listeria  spp. 
should be conducted with regulatory oversight.  Th is review should take into account previous 
environmental and end-product testing resu lts.  If the review indicates that Listeria  spp. are not 
being controlled, increased environmental samp ling should be undertaken by the processor to 
determine whether Listeria  spp. are present.  If Listeria  spp. are present, this  should be taken as  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   11 
 evidence for the need to improve control of Listeria spp.  In addition, if  food contact surface 
(FCS) samples are found positive at two (Category 1; see Figure 1) or more (Category 2A and 
2B; see Figure 2) steps, end-produc t testing should be in itiated to ensure that finished product is 
not contaminated with L. monocytogenes.  
 
 
6.2.1.2. Product control: 
 
Increased knowledge of the ecology of L. monocytogenes  in RTE food products has clarified 
which products can or cannot support the growth of L. monocytogenes.   This has permitted the 
classification of RTE foods for which specific co mpliance action may be needed. The nature of 
concern should be determined based on the info rmation in Table 1. Sampling priority should be 
given to Category 1 RTE products. Although Categor y 2A and 2B products are of lesser concern 
than Category 1 RTE foods, sampling at times ma y still be warranted.  RTE food processors, in 
consultation with the regulatory authority, should  a) attempt to determine the source of the 
contamination (e.g., root cause analysis) usi ng inspection, environmental sampling and end-
product testing, and b) take the appropriate correc tive actions.  The actions taken need to reflect 
the findings of the investigation that is done when unsatisfactory results are obtained.  They may 
include, without being limited to, the following:  i) increasing and/or correcting sanitation 
procedures (including equipment disassembly be yond FCSs with intensified cleaning/sanitation 
and verification of the cleaning/sanitation process and intense cleaning/ sanitation of surrounding 
area) and modification of equipment for impr oved cleanability; ii) observing GMPs during 
sanitation and operations to ensu re compliance; iii) requiring mi nimum follow-up tests (Figures 
1, 2 and 3); iv) obtaining additi onal data to confirm hypothese s when conducting root cause 
analysis; v) developing and impl ementing an enhanced sampling pl an (for the affected line and 
possibly the product); and vi) if applicable, revisiting the HACCP system and adjusting it, if 
necessary.  Corrective actions must be monitored to confirm their effectiveness.  The whole process should be documented, as this informati on can be integrated into the establishment’s 
trend analysis activities.  
  
6.2.2. Imported RTE products: 
 
Canadian food importers must import food produc ts that are in compliance with relevant 
Canadian legislation and policies. The importer should be able to demonstrate that the food 
products are safe and meet these requirements.  Information regarding the product(s) imported, 
including information about the su pplier, processor or exporter is  most useful, and should serve 
as background information to determine what veri fication activities are required.  As well, the 
importer should ensure that safe food storage and handling procedures are in place at the 
importer's facility. 
 Inspection of imported RTE foods is intended to ensure an equivalent level of protection to 
consumers of both imported and domestic produc ts.  Canadian food regulatory agencies, 
however, may be unable to evaluate whether ce rtain imported foods have been manufactured 
using effective GMPs and/or the HACCP system. Th erefore, other verification measures such as  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   12 
 end-product testing may be required to assess whethe r these products meet th e criteria in Table 1.  
If insufficient, inadequate or no information exis ts regarding the 2A or 2B categorization of the 
imported RTE product (i.e., RTE food in wh ich a limited potentia l for growth of L. 
monocytogenes to levels not greater than 100 CFU/g can occur or in which growth of L. 
monocytogenes cannot occur throughout its shelf-life, as determined by validated data), it will, 
by default, be considered as a RTE food in which growth of L. monocytogenes  can occur (i.e., 
Category 1).  Hence, the sampling plan and method of analysis for Category 1 foods, as specified 
in Table 1, will be applied.  If questions arise, it is the responsibility of the importer to demonstrate what category the RTE food belongs to.  Compliance action may be taken against 
lots that exceed the criteria.    Compliance action should be taken on a lot-by-lo t basis and should not differ from that for 
domestic products.  Importers should have a system  in place to ensure th at Canadian regulatory 
authorities will be able to differentiate individu al lots based on clear product markings.  If a 
shipment cannot be distinguished into individu al lots, then the enti re shipment would be 
considered as a single lot for oversight and comp liance activities.  The sampling plan should be 
adjusted accordingly.   
6.2.3.  Exported RTE products: 
 
Canadian food exporters are responsible for expo rting food products that meet the requirements 
of the receiving country, as well as the provisions of Section 37 of the Food and Drug Act  
(Government of Canada, 2010a).     
 7    Achieving Compliance with th e Criteria for Ready-to-Eat Foods 
 
7.1 Requirements for the Manufacture of Ready-to-Eat Food Products  
 
The policy is based on a combination of manuf acturing verification and control measures (by 
industry), oversight (by regulat ory authorities), as well as environmental sampling and end-
product testing that should be undertaken by both industry and regulat ory authorities.   
 
RTE food processors should implement adequate verifications and controls to ensure their 
products are in compliance with the criteria in Ta ble 1. It should be assumed that some incoming 
raw ingredients may contain L. monocytogenes. Thus, when feasible, RTE food processors 
should apply procedures that are validated to eliminate or reduce L. monocytogenes  in the raw 
materials in order to comply with the criteria for L. monocytogenes in RTE foods. The potential 
for recontamination with L. monocytogenes should also be controlled and  is influenced by factors 
such as plant layout (including traffic control), infrastructure, equipment design and maintenance 
(e.g., equipment that require disassembly, such as slicing equipment), effec tiveness of sanitation 
procedures and employee practic es (CAC, 2007; Meat Industry Listeria monocytogenes Working 
Group, 2010).  
  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   13 
 The survival of L. monocytogenes can be managed through the HACCP system, which includes 
the use of validated critical control points ( CCPs) and appropriate monitoring and verification 
procedures for each CCP. Procedures for validati ng pathogen reduction steps and strategies such 
as the use of additives to prevent growth have  a long history of use for a variety of foodborne 
pathogens. The concern for recontamination is managed through the application of GMP 
procedures, including adequate  sanitation practices, which require thorough and regular 
adherence due to the prevalence of L. monocytogenes in the environment, eas e of dispersal, and 
ability to grow in the RTE processing environment (Meat Industry Listeria monocytogenes 
Working group, 2010).  Several documents are available for guidance (Tompkin et al. , 1999; 
NFI/NFPA, 2002; CAC, 2007; Meat Industry Listeria monocytogenes Working group, 2010). In 
addition, workshops sponsored by industry trade asso ciations can be very effective for teaching 
current best practices for Listeria  control within specific segments of industry. 
 
Also helpful to food processors is direct on-sit e observation which is a valuable means to assess 
compliance with the GMPs that can influence the presence of Listeria  spp. (CAC, 2007).  It is 
not possible, however, to predict by direct on- site observation alone, the degree to which Listeria  
spp. may occur in areas where RTE foods are ex posed before and during final packaging.  Many 
existing food processing establishments were not originally designed for the control of pathogens 
with the unique ch aracteristics of L. monocytogenes .  However, each food processing 
establishment should be managed following best practices, recognizing that  the verification and 
control of Listeria  spp. is necessary for consumer protec tion.  Modifications can often be made 
to control Listeria  spp. in the environment and to reduce the risk of product contamination. An 
effective environmental monitoring program, s upported by investigative sampling to detect 
sources of Listeria  spp., should be used to identify the ch anges that will faci litate the control 
needed to ensure compliance with the criteria (T able 1). Experience indicates that environmental 
sampling is the most sensitive tool to assess control of the environment and risk of product contamination (Tompkin et al. , 1992; Tompkin, 2002).   
 
 
7.2 Environmental Sampling (Figures 1, 2 and 3) 
Steps for sampling FCSs and RTE foods (Figures  1 and 2) as well as non-FCSs (Figure 3) by 
processors and regulatory author ities are outlined in  this section.  Environmental sampling 
should be conducted according to MFLP-41 (H ealth Canada, 2010e).  Testing should be 
conducted according to any method published in the Health Canada’s Compe ndium of Analytical 
Methods for Listeria  in which the “application” section is  appropriate for the intended purpose 
(e.g., MFHPB-methods and MFLP-methods).  The rela tive importance of veri fying control of the 
processing environment should be reflective of the risk to consumers if the food becomes 
contaminated. Of highest concern are i) foods th at do not contain validated inhibitors of the 
growth of L. monocytogenes  (e.g., lactate, diacetate); ii)  foods in which growth of L. 
monocytogenes to levels >100 CFU/g can occur during th e shelf-life of the food; iii) foods which 
are not subjected to a listericid al treatment in the package befo re distribution and; iv) foods 
which are targeted to a high-risk  population group.  The same factors should be considered when 
establishing the frequency and extent of sampling of the environment. Particularly for foods in 
which L. monocytogenes  can grow during the product’s shelf-life, the monitoring and control  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   14 
 programs should be sufficiently strong (e.g., re garding sampling selection, frequency of 
sampling, numbers of samples, method of sampli ng, etc.) to enable RTE food processors and 
regulatory authorities to conclude  when reviewing the data that the foods being produced are not 
contaminated with L. monocytogenes  (CAC, 2007; Meat Industry Listeria monocytogenes 
Working Group, 2010). 
 Each establishment’s Listeria  control program should be designe d to reflect current knowledge 
and experience that L. monocytogenes  can be reduced to a level in the environment that ensures 
product will not become contaminated.  Ho wever, the possibility exists that Listeria  will be re-
introduced into areas in which RTE foods are exposed. These factors em phasize the need to 
maintain an environmental sampling program that is adequate to manage consumer risk in relation to the Category of RTE food being produced (Table 1). It is important to continually 
strive for negative results by responding to ea ch positive sample with appropriate corrective 
actions in a timely manner.   Establishments processing RTE foods should design, implement and maintain an environmental sampling program for testing FCS and non-FCS for the presence of Listeria  spp.  It is 
recommended that Listeria  spp. should be monitored in the environment as outlined in Figures 1, 
2 and 3.  Testing for Listeria  spp. and reacting to positive results as if they were L. 
monocytogenes provides for a more sensitive and broade r verification and control program, than 
would testing for L. monocytogenes  alone (Meat Industry Listeria monocytogenes Working 
group, 2010).  The purpose of the environmental sa mpling program is to assess the effectiveness 
of sanitation and other GMPs in RTE proces sing environments and the potential for product 
contamination.  In addition, by detecting and re sponsibly responding to each positive result, 
consumer risk can be minimized. Environmen tal monitoring programs must include routine 
sampling of FCSs that come in to contact with exposed RTE fo ods before final packaging.  
Sponge/swab samples from surface areas of equi pment should be collected during production, 
typically after 3 hours of start up of operation.  Guidance for environmental sampling can be 
found in the Health Canada’s Compendium of  Analytical methods, under MFLP-41 (Health 
Canada, 2010e).  The number of sites (e.g., 1 – 10 ) will vary according to the complexity of the 
processing system or packaging line. The freque ncy and points of sampling for routine sampling 
should be plant and/or line specific, based on th e manufacturing processes and the controls that 
are present (Tompkin et al. , 1992).  An increase in sample  sites (FCSs and non-FCSs) and 
frequency should be considered during and/or af ter special circumstances  (e.g., construction, the 
installation of used or modified  equipment,  overhead/ceiling leaks in exposed product areas), 
which may provide an oppor tunity for control of L. monocytogenes  to be lost.   
 In some situations, food in various stages of  processing or product build-up can be used as 
additional samples to furt her assess the presence of Listeria  along a processing line or system. 
Samples should also be collected from non-FCSs  as an additional measure of verification.  
Recent publications (CAC, 2007; Meat Industry Listeria monocytogenes Working Group, 2010) 
can provide guidance on the establishment of an environmental sampling program. 
 Investigational sampling differs from the routine environmental pr ogram used to monitor control 
of Listeria.  It involves collecting additional samples from  sites to help identify more clearly the  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   15 
 source(s) of contamination. Investigational sampling is a valuab le tool for identifying and 
eliminating harbourage sites (Tompkin, 2002; CAC, 2007). The benefit of environmental 
sampling for products given a validated final in-package listericidal treatm ent is affected by the 
degree of inactivation delivered by the listericidal process, e.g., cook-in-bag roast beef. 
 Tompkin et al., (1999) as well as D’Amico and Donnelly (2008) found that in general, non-FCS 
contamination with Listeria  spp., including L. monocytogenes , usually precedes FCS 
contamination, thereby highlightin g the importance of environmenta l verification and controls.  
Therefore, finding sources of contamination away from the production line and preventing cross-contamination, is encouraged as  a fundamental principle of Listeria  control.  The guidance 
provided in Figures 1, 2 a nd 3 should be followed.  
 Depending on the application of the sampling pr ogram (i.e., the amount of testing being done, 
and the locations(s), number and frequency of positive findings), the presence of L. 
monocytogenes in a RTE food will (i.e., in Category 1 RTE foods) or would likely (i.e., in 
Category 2 RTE foods) indicate th at the establishment’s control program is not adequate to 
prevent product contamination.  When reviewing data for trend analysis, contamination of non-FCSs with Listeria  spp. in areas of the plant environmen t where RTE foods are exposed to post-
lethality contamination as applicable, could indicate that the control of Listeria  is inadequate. It 
is the responsibility of processors of RTE food to react to a ll unsatisfactory environmental results 
in a timely manner and to ultimately achieve Listeria -negative results.  A finding of Listeria spp. 
in the RTE processing environment should trigge r follow-up actions, e .g., corrective actions 
which include intensified cleaning and sanitizin g, timely re-testing of the contaminated area, 
testing of end-products that were potentially in contact with the positive FCS, in-depth review of the plant’s food safety system, etc., as appropriate.  If two or more samples from the same production  line (i.e., using the same equipment) are found 
positive within a short timeframe, this is considered to be evidence of persistent contamination and an indication that the Listeria  control program could be inadequate. Persistent contamination 
of FCS with any Listeria  spp. in the RTE plant environment c ould be an indication of inadequate 
GMPs and sanitation practices. Appropriate follo w-up actions are necessary when unsatisfactory 
results are obtained, taking into account the type and/or location of the sampling sites, and the 
category of food (see Figures 1, 2 and 3).    All positive results for L. monocytogenes  in a RTE food or persistent Listeria  spp. on a FCS, 
should be communicated as soon as possible to the regulatory authority having jurisdiction, as 
per Figures 1 and 2.   
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   16 
  
Figure 1:  Sampling Guidelines for FCSs  and Category 1 Ready-to-Eat Foods  
 
Step A  
 
 YES FCS positive for Listeria  spp.? 
FCS positive for Listeria 
spp.? Test product as per Table 1.  
NO NO  Continue routine 
monitoring 
program. • Collect FCS samples, as per MFLP-41. 
• Analyze 10 FCS samples, either individually or as composites a, b. 
• Use any method published in the Health Canada ’s Compendium of Analytical Methods for Listeria  spp. (e.g., MFHPB-
30; see Appendix D)c. 
Resume routine 
monitoring program and 
release product 
put on hold at 
Step B. YES • Initiate corrective actions as soon as possiblee. 
• After corrective actions are implemented: 
o All products from that lin e should be placed on hold. 
o Collect FCS samples f to verify efficacy of corrective actions, as per MFLP-41. 
o Analyze FCS samples individually. 
o Use any method published in the Health Canada ’s Compendium of Analytical Methods for Listeria spp. (e.g., 
MPFPB-30; see Appendix D)c. 
L. monocytogenes  detected 
in 125 g g.
Consult with regulatory 
authority about disposition 
of product. Consult with regulatory 
authority.  An HRA may 
be requested.  L. monocytogenes  not 
detected in 125g. Step Bd 
  Product    Testing Environmental      Testing 
YES 
Step C • Notify regulatory authority as soon as possible. 
• Repeat Step B until FCS samples are negative for Listeria spp. and  product samples are negative for L. monocytogenes h. 
• Collect FCS and product samples until 3 or more consecutive production days of FCS sample s (taken in Step B) are 
negative, and product samples do not exceed criteria in Table 1. If  any FCS sample is positive for Listeria spp. or product 
samples exceed criteria in Table 1, review previous correctiv e actions, consider other options and continue investigative 
actions.  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   17 
 a      The number of meaningful sampling sites (preferabl y 10) selected on each processing  line should depend upon the 
complexity of the line(s).  
 
b   If compositing more than 10 FCS sites, a protocol should be developed and validated.  The number of swabs and the 
enrichment protocol ma y vary according to the processing conditions.  
 c     In addition, the “application” section must be appropriate for the intended purpose (e.g., MFHPB and MFLP methods).   
 
d     Events that proceed beyond Step A should be recorded and maintained in a file that is separate from the routine 
monitoring program data.   The records should include in formation on corrective actions, investigational sampling, 
product testing and disposition of product.  
e    Investigative sampling can assist in finding and correcting the source of contamination, particularly if a harbourage 
site exists within equipment which leads to isolation of a Listeria spp. or a specific subtype of L. monocytogenes  (CAC, 
2007).   
 f     At a minimum, the FCS sites in the routine monitoring program should be included.  The number and location of samples should be adequate to verify that the entire line is negative and under control.   
 g     It is recommended that subsequent lots be held.  If L. monocytogenes  is detected on product at Step B, all 
subsequent lots of product should be tested. 
 
h     After corrective actions have been implemented at Step C, it is recommended that each lot of product should be held and tested until the results demonstrate that control has been achieved. 
 
Note 1:  This policy states the minimum requirements that sh ould be adhered to.  The operator or regulatory authority 
can exceed these minimum requirements. 
 
Note 2:  End-product testing for L. monocytogenes  should be performed if any L. monocytogenes  is found on a FCS(s).  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   18 
 Figure 2:  Sampling Guidelines for FCSs  and Category 2 Ready-to-Eat Foods  
  
• Collect FCS samples, as per MFLP-41.  
• Analyze 10 FCS samples, either individually or composites a, b. 
• Use any  method published in the Health Canada ’s Compendium of Analytical Methods for Listeria spp. (e.g., MPFPB-
30; see Appendix D)c.  
 
 Step A 
 
FCS positive for Listeria 
spp.? Test product, as per Table 1. 
L. monocytogenes  exceeds 
100 CFU/g. L. monocytogenes  does not 
exceed 100 CFU/g. 
Consult with regulatory 
authority about disposition 
of product.   Consult with regulatory authority.  An HRA may be requested.   No
YES Product  
Testing Resume routine 
monitoring program. 
  
YES • Initiate corrective actions as soon as possiblee. 
• After corrective actions are implemented:  
o Collect FCS samples f to verify efficacy of corrective actions, as per MFLP-41. 
o Analyze FCS samples individually. 
o Use any method published in the Health Canada ’s Compendium of Analytical Methods for Listeria  spp. (e.g., 
MPFPB-30; see Appendix D)c. 
YES 
Resume routine 
monitoring program 
and release product put 
on hold at Step C. • Initiate intensified corrective actions as soon as possiblee.  
• After intensified corrective actions are implemented:  
o All products from that line should be placed on hold.  
o Collect FCS samplesf to verify efficacy of corrective actions, as per MFLP-41. 
o Analyze FCS samples individually. 
o Use any  method published in the Health Canada ’s Compendium of Analytical Methods for Listeria spp. (e.g., MPFPB-30; 
see Appendix D)c in FCS samples. 
                                          
Environmental Testing Step C FCS positive for Listeria spp.?NO YES NO FCS Positive for Listeria  spp.? Continue routine 
monitoring program. 
Step Bd 
Step D • If positive FCS or product samples continue to be detected, determine whether the positives are due to processing conditions th at can not 
eliminate Listeria  spp. in the raw material(s).  If the answer is yes, a request for an HRA from Health Canada may be appropriate.  
• If the positive FCS samples are due to re-contamination, continue intensified actions until FCS samples are negative.  
• Review all results with regulatory authority.  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   19 
 a     The number of meaningful sampli ng sites (preferably 10) selected on each  processing line should depend upon the 
complexity of the line(s).  
 
b     If compositing more than 10 FCS sites, a protocol should be developed and validated.  The number of swabs and the enrichment protocol may vary according to the processing conditions.  
 
c     In addition, the “application” section must be appropriate for the intended purpose (e.g., MFHPB and MFLP methods).   
 
d     Events that proceed beyond Step A should be recorded and maintained in a file that is separate from the routine 
monitoring program.  The records should include information on corrective actions, investigational sampling, product 
testing and disposition of product. 
 
e     Investigative sampling can assist in finding and correcting the source of contamination, particularly if a harbourage 
site exists within equipment which leads to isolation of Listeria spp. or a specific subtype of L. monocytogenes  (CAC, 
2007). 
 
f    At a minimum, the FCS sites in the routine monitoring program should be included.  The number and location of samples should be adequate to verify that the entire line is negative and under control.   
 
Note 1:  This policy states the minimum requirements that sh ould be adhered to.  The operator or regulatory authority 
can exceed these minimum requirements. 
 
Note 2:  End-product testing for L. monocytogenes  should be performed if any L. monocytogenes  is found on a FCS(s).    
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   20 
 Figure 3:  Sampling Guidelines for non-FCSs, especially those in proximity to FCSs, linked 
to RTE foods in Category 1 and 2  
 
Step A • Collect samples from non-FCS, as per MFLP-41. 
• Analyze 10 non-FCS samples, either individually or composites a, b. 
• Use any method published in the Health Canada’s Compendium of Analytical Methods for 
Listeria  spp. (e.g., MFHPB-30; see Appendix D)c.  
   
 
Non-FCS positive for Listeria  spp.? NO 
YES Continue 
routine 
monitoring 
program.  
Step B 
NO Resume routine 
monitoring 
program.
 
YES Non-FCS positive for Listeria  spp.? • Initiate corrective actions as soon as possible and perform investigative samplingd. 
• After corrective actions: 
o Collect samples from non-FCS to veri fy the efficacy of corrective actionse, as per 
MFLP-41. 
o Analyze non-FCS samples individually.  
o Use any method published in the Health Canada’s Compendium of Analytical Methods 
for Listeria  spp. (e.g., MFHPB-30; see Appendix D)c. 
Step C • Repeat Step B until non-FCS samples are negative for Listeria  spp. 
 
Note : If non-FCS samples are found positive for Listeria  spp. on a regular basis, especially those 
which are near to FCSs, FCS shou ld be tested more frequently. 
  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   21 
 a      The number of meaningful sampling sites (preferably 10) selected in the plant should depend upon the complexity 
of the plant.  
 
b     If compositing more than 10 non-FCS sites, a protocol should be developed and validated.  The number of swabs and the enrichment protocol may vary according to the processing conditions.  
 
c     In addition, the “application” section must be appropriate for the intended purpose (e.g., MFHPB and MFLP methods).   
 
d     Investigative sampling will assist in finding and corr ecting the source of contamination.  For instance, current 
sanitation activities may be ineffective, in which case a harbour age site may be present.  This may be inferred from the 
isolation of a specific subtype of L. monocytogenes  (CAC, 2007). 
 
e     It should be noted that it is not necessarily only  the same sample sites that should be tested after corrective actions.  
Upon re-sampling, the original or nearby sites might be negative but sampling other sites might reveal a positive, and 
hence be more informative in resolving the problem.   
 
 
  
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   22 
 7.3        Sampling and Analysis of Finished Ready-to-Eat Foods 
 
For most RTE products, control (i.e., by adequate  sanitation and GMPs) and verification of the 
environment (i.e., by an appropriate  environmental sampling plan) is  the most desirable approach 
to verification and control of  L. monocytogenes.  Therefore, a better decision can be made 
regarding releasing end-products, rather than relying on testing individual lots.  In fact, 
microbiological testing of food is an impreci se science and may not portray the true 
microbiological condition of the food.  Consequently, for many foods, the relative importance of 
end product testing is less than that for environmental testing.  However, end-product testing is 
conducted for various reasons, such as cust omer requirements, evaluation of product 
contamination when FCS tests positive for Listeria spp. (as stipulated in Figures 1 and 2), 
periodic testing to determine control of proce ss/GMPs, foreign country requirements, regulatory 
testing, verification of the e ffectiveness of the antimicrobi al treatments, incoming product 
testing, testing of marketed products  as part of an inve stigation and trend an alysis, etc.  When 
testing end-products, RTE food pr ocessors should develop:  
 
a) written procedures for end-product testing wi th details on any hold and test procedures 
b) sampling procedures 
c) sampling frequency and size  
d) methodology and  
e) proposed follow-up actions. 
 
It is recommended that all implicated end-products be held pendi ng results from routine testing, 
as per Table 1 “Sampling methodolog ies and compliance criteria for L. monocytogenes in ready-
to-eat (RTE) foods”.  End-product testing for L. monocytogenes  should be performed if any L. 
monocytogenes is found on a FCS(s).  
 Samples of all finished RTE food produc ts submitted for the analysis of L. monocytogenes will 
consist of 5 sample units of at least 100 g each (T able 1), which are representative of the lot and 
the production conditions, taken at random from each  lot.  Sampling of imports, particularly of 
large shipments, should be applied to identifiab le lots of the product. Where the importer is 
unable to provide information on the identity of different lots, then the entire shipment (e.g., per 
product type) would be treated as a single lot.   
  
Category 1 RTE foods: 
 
Analysis of Category 1 RTE foods for the presence of  L. monocytogenes should be conducted 
using any method published in the Health Canada ’s Compendium of Analytical Methods for L. 
monocytogenes in which the “application” section is appropriate for the intended purpose (e.g., 
MFHPB methods and MFLP methods).  An analy tical sample size of 5 X 25g for this specific 
category of RTE product should be used for rout ine end-product testi ng.  The detection of L. 
monocytogenes in a finished Category 1 RTE food requires follow-up as described in step C of 
Figure 1.    
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   23 
 Category 2A and 2B RTE foods: 
 
For the analysis of all Category 2 RTE foods, a quantitative analysis should be conducted 
according to, for example, Laboratory Procedur e (MFLP) 74 (see Appendix E), or any method 
published in the Health Canada’s Comp endium of Analytical Methods for L. monocytogenes  in 
which the “application” section is appropriate for the intend ed purpose (e.g., MFHPB-methods 
and MFLP-methods).  An analytical sample size of 5 X 10g for this specific category of RTE 
product should be used for routine end-product testing.  This will determine the CFU/g of L. 
monocytogenes in the food,  above the action level (i.e., 100 CFU/g).  The detection of L. 
monocytogenes in a finished Category 2 RTE food requires follow-up as described in steps C and D of Figure 2.  The frequent presence (i.e., occurring repeatedly at brief intervals) of L. 
monocytogenes at low levels ( ≤ 100 CFU/g) in a product could be  an indication of inadequate 
application of GMPs, and/or a process that  cannot ensure non-de tectable levels of L. 
monocytogenes.   
Follow-up actions: 
 
The appropriate regulatory authority should be notified upon any positive end-product results, 
and follow-up actions should be implemented to ensure that the RTE food processor has the 
situation (i.e., including all imp licated RTE end-products) under c ontrol.  Corrective actions to 
be undertaken by the company and/or regulatory authorities, such as a review of the company’s Listeria  control strategy including GMPs, intensive cl eaning and sanitation, as well as additional 
environmental and end-product testin g, are all strongly recommended.   
 
 
                    
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   24 
 Table 1: Sampling Methodologies  and Compliance Criteria for L. monocytogenes in Ready-
to-Eata Foods  
 
Categories Sampling Analysis Type of 
analysis Action level 
for L. 
monocytogenes  Nature 
of 
concern Level of 
priority 
for 
oversightb 
1.  RTE foods in which growth 
of L. monocytogenes can 
occurc  throughout the stated 
shelf-life, e.g., durable life date 
shown as a “best before” date 
on the package (e.g.d, deli-
meats, soft cheeses, hot dogs, pâté).  5 sample units (min 100 g or ml each), which are representative of 
the lot and the 
production conditions,  taken  aseptically at random from each lot 5 x 25 g analytical units
e are 
either 
analysed 
separately or compositedEnrichment only Detected in 
125g  
f, g Health Risk 1
h High 
2 A) RTE foods in which a 
limited potential for growth of L. monocytogenes  to levels not 
greater than 100 CFU/g can 
occur
c throughout the stated 
shelf-life (e.g., durable life date shown as a “best before” date on the package).  A number of factors will be taken into consideration with regards to which foods may fall into this 
Category (see Section 6.1): 
Such foods could include: refrigerated gravlax/cold-smoked rainbow trout and 
salmon, fresh-cut produce, etc. 
 
2 B) RTE foods in which 
growth of L. monocytogenes  cannot occuri throughout the stated shelf-life, e.g., durable 
life date shown as a “best 
before” date on the package (e.g., ice cream, hard cheese, dry salami, dried-salted fish, varieties of prosciutto ham).  Same as above 5 x 10 g 
analytical units
e  Direct plating only > 100 CFU/g  
j, 
k, l  Health 
Risk 2h, l  Medium 
to low  
 
  
 
 
 
  
 
   
 
 
Low
   
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   25 
 a-  For a definition of RTE foods, see Appendix A. 
 
b-  Other criteria (e.g., process, packaging, outbreak data) could also have an impact on the level of priority assigned 
to the RTE food products.  
 
c-  For a definition of RTE foods in which growth of L. monocytogenes can occur, see Appendix A. 
 
d- These traditional examples of Category 1 foods may fall into Category 2A or 2B, if it can be demonstrated that 
they do not support the growth or support limited growth of L. monocytogenes  to levels not greater than 100 CFU/g 
throughout the stated shelf-life (e.g., durable life date  shown as a “best before” date on the package).  
 
e-  The designated analytical unit is taken from each sample unit. 
 
f-  For example, MFHPB-30; presence or absence by enrichment only (see Appendix D), or use any enrichment 
method for L. monocytogenes  published in the Health Canada’s Compendium of Analytical Methods in which the 
“application” section is appropriate for the intended purpose (e.g., MFHPB methods and MFLP methods). 
 
g- Assuming a log-normal distribution, this sampling plan would provide 95% confidence that a lot of food 
containing a geometric mean concentration of 0.023 CFU/g and an analytical standard deviation of 0.25 CFU/g would be detected and rejected if any of the five samples are positive for L. monocytogenes (CAC, 2009a). 
 
h-  For a definition of health risk categories, see Appendix A. 
 
i- For a complete definition of “RTE foods in which growth of L. monocytogenes  will not occur”, see Appendix A  
 A RTE food in which growth of  L. monocytogenes will NOT occur (CAC, 2009a) includes the following:  
 (a) pH < 4.4, regardless of a
w 
 (b) a w < 0.92, regardless of pH 
 (c) combinations of factors (e.g., pH < 5.0 and a w < 0.94) 
 (d) frozen foods       The pH and a
w should be determined for at least 3 out of 5 analytical units. The growth of L. 
monocytogenes is presumed to occur, if any one of the analy tical units falls outside the range of pH and a w 
values in which the growth of L. monocytogenes will not occur (as above).   
 
j- For example, MFLP-74; enumeration done by direct plating onto selective agar (see Appendix E), or use any enumeration method for L. monocytogenes  published in the Health Canada’s Compendium of Analytical Methods in 
which the “application” section is appropriate for the intended purpose (e.g., MFHPB methods and MFLP methods). 
 
k- Assuming a log-normal distribution, this sampling plan would provide 95% confidence that a lot of food 
containing a geometric mean concentration of 93.3 CFU/g and an analytical standard deviation of 0.25 log CFU/g would be detected and rejected based on any of the five samp les exceeding 100 CFU/g L. monocytogenes (CAC, 
2009a). 
 
l-  This becomes a Health 1 concern if the RTE food is intended to be produced for a high-risk population group 
such as the elderly, pregnant women or immunocompromised individuals (AIDS patients, transplant recipients, cancer patients, etc.), or if the product is intended for use in a Category 1 product.  In addition, if counts ≤ 100 
CFU/g are detected in RTE products intended to be produc ed for high-risk population groups such as those outlined 
above, an HRA may be requested, which may l ead to a higher health risk concern.    
 
Note:  If insufficient, inadequate or no information exis ts regarding the 2A or 2B categorization of the RTE food 
product (i.e., domestic or imported RTE foods in which a limited potential for growth of L. monocytogenes  to levels 
not greater than 100 CFU/g can occur or in which growth of L. monocytogenes  cannot occur throughout its stated 
shelf-life, as determined by validated data), it will by de fault, be considered as a RTE food in which growth of L. 
monocytogenes can occur (i.e., Category 1).  Hence, the sampling plan and method of analysis for Category 1 foods, 
as specified in Table 1, will be applied.  If questions arise, it is the responsibility of the processor/importer to 
demonstrate which category the RTE food belongs to.    
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   26 
 7.4 Importance of Trend Analysis and Quality Assurance Tools  
 
An establishment cannot rely solely on e nd-product testing to verify and control Listeria .  Its 
food safety management system should apply modern quality control and statistical methods to 
monitor its processes and detect time and/or spat ial patterns (trends) suggestive of contamination 
sources that can be further investigated and mitig ated.  In addition, these trends (data) can be 
used comprehensively to model and predict risk and thus better target oversight and compliance 
activities.  Where possible, qua lity control and statistical methods should include modern 
graphical techniques such as control charts, Pa reto diagrams, etc., as  well as appropriate 
descriptive and analytical  statistical methods.  All data and analysis results should be made 
available to those in the plan t responsible for managing the Listeria  control program. 
Responsibility for updating and disseminating the data should be assigned to one or more 
individuals within th e establishment (e.g., quality assura nce, food safety and/or HACCP 
coordinators).  On-going review  and analysis of the data for Listeria spp. from routine 
monitoring programs should be performed to detect  trends before major issues develop.  Such 
reviews also provide inform ation on the prevalence of Listeria  spp., their fluctuations over time 
and identify issues to be addr essed in a timely manner.  Attent ion should be given to the dates 
and locations of positive samples to determine if low level and/or sporadic positives occur at 
certain locations that may have gone unnoticed previously (CAC, 2007). Trend analysis should 
be used to achieve improved control over time as each establishment gains experience in 
controlling Listeria  and makes appropriate adjustments. 
 
 
8 Development of Educational Materials for Consumers and Others Involved in  Food 
Handling and Preparation 
 
The aim of developing educational materials is to educate, inform and increase awareness of 
food hazards associated with RTE foods for cons umers in general, and more specifically for 
seniors and their caregivers, pr egnant women, people with weakened immune systems and other 
potentially high-risk individuals  about safe food handling practic es, and what they can do to 
reduce the risk of acquiring foodbor ne listeriosis.  While significan t information already has been 
provided by various levels of government , collaboration between the federal and 
provincial/territorial and municipal governments, will ensure that consumers receive reliable and 
consistent information so that they can make better informed choices and/or learn how foods 
should be properly handled and prepared.  To this  end, Health Canada will seek the collaboration 
of the PHAC, the CFIA and the Provinces/Ter ritories for future work in this area. 
 
 8.1 Contributions of Health Canada Scientists to Pub lished Information Related to              
      Foodborne Listeriosis 
   
$ Clark, C.G., Farber, J.M., Pagotto, F., Ciampa, N., Doré, K., Nadon, C., Bernard, K., Ng, 
L.-K. and the Canadian Public Health La boratory Network.  (2010).  Surveillance for 
Listeria monocytogenes and listeriosis in Canada, 1995- 2004.  Epidemiol. Infect., 138: 
559-572.  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   27 
 $ Farber, J.M., Pagotto, F. and Scherf, C.  (2007).  Incidence and behaviour of Listeria 
monocytogenes in meat products.  In: Listeria, Listeriosis and Food Safety .  Ryser E. T. 
and Marth E. H. (Eds.), 3rd ed ition, CRC Press. Pages:  503-570.  
 
$ Pagotto, F. Corneau, N. and Farber, J.M.  (2006).  Listeria monocytogenes infections.  In: 
Foodborne Infections and Intoxications .  Riemann, H.P. and Cliver, D.O. (Eds.), 3rd 
edition, Academic Press.  Pages: 313-340. 
$ Pagotto, F., King, L-K, Clark, C. Farber, J.M. and the Canadian Public Health Laboratory 
Network.  (2006).  Canadian Listeriosis Reference Service.  Foodborne Pathog. Dis., 
3:132-137. 
$ ILSI Expert Panel.  (2005).  Achievi ng continuous improvement in reductions in 
foodborne listeriosis - a risk based approach.  J. Food Prot., 68:1932-1994.  
$ Farber, J.M., Daley, E.M., Mackie, M.T. and Limerick, B.  (2000).  A small outbreak of 
listeriosis potentially linked  to the consumption of imitation crab meat.  Lett. Appl. 
Microbiol., 31:100-104. 
$ Farber, J.M. and Harwig, J.  (1996).  The Canadian Position on Listeria monocytogenes 
in Ready-to-eat Foods.  Food Control, 7: 253-258. 
$ Farber, J.M., Ross, W.H. and Harwig, J.   (1996).  Health Risk Assessment of Listeria 
monocytogenes in Canada.  Int. J. Food Microbiol., 30:145-156 
$ Lammerding, A.M. and Farber, J.M.  (1994).  The Status of Listeria monocytogenes in 
the Canadian Food Industry.  Dair y, Food Environ. Sanit., 14: 146-150. 
$ Farber, J.M.  (1993).  Current Research on Listeria monocytogenes in Foods:  an 
Overview.  J. Food Prot., 56:640-643.  
  
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   28 
 Appendix A: Definitions 
 Durable life: 
 
Section B.01.001 of Division 1, Part B (Foods) of the Food and Drugs Regulations  defines 
"durable life" as follows:  “ Durable life means the period, commencing on the day on which a 
prepackaged product is packaged for retail sale , during which the product, when it is stored 
under conditions appropriate to th at product, will retain, without  any appreciable deterioration, 
its normal wholesomeness, palatability, nutritiona l value and any other qualities claimed for it 
by the manufacturer” (durée de conservation)  (Government of Canada, 2010b).   
 Durable life date: 
 
Section B.01.001 of Division 1, Part B (Foods) of the Food and Drugs Regulations  defines 
"durable life date" as follows:  “Durable life date means the da te on which the durable life of a 
prepackaged product ends” (date limite de c onservation) (Government of Canada, 2010b).  
 Food additives: 
 
Section B.01.001 of Division 1, Part B (Foods) of the Food and Drugs Regulations  defines "food 
additive" as follows:  "Food additive means any substance the use of which results, or may 
reasonably be expected to result, in it or its by-products becoming a par t of or affecting the 
characteristics of a food, but does not include: (a ) any nutritive material t hat is used, recognized 
or commonly sold as an article or ingredient of  food; (b) vitamins, mi neral nutrients and amino 
acids, other than those listed in the tables to Division 16; (c) spi ces, seasonings, flavouring 
preparation, essential oils, oleoresins and natural  extractives; (d) agricultural chemicals, other 
than those listed in the tabl es to Division 16; (e) food packaging materials and components 
thereof, and (f) drugs recommended for administra tion to animals that may be consumed as 
food" (additifs alimentaires) (Health Canada, 2007; Government of Canada, 2010b). 
 Food additives are regulated in Canada under the Food and Drugs Act and Regulations , and, 
they must therefore be listed in  the Tables in Division 16 of the Regulations  to be permitted for 
use.  If the Regulations do not allow use of a particular food additive, the processor is required to 
file a food additive submission in acco rdance with Section B.16.002 of the Regulations before it 
can be used in foods sold in Canada.  In some  instances, the commercial use of a previously 
approved food additive in a new application may be enabled by an Interim Marketing 
Authorization (IMA), pursuant  to section B.01.056 of the Regulations. An IMA provides a 
mechanism for bridging the time between acceptan ce of a submission and publication of the final 
regulatory amendments in Canada Gazette Part II .  An IMA becomes effective upon its 
publication in Canada Gazette Part I  (Health Canada, 2007; Health Canada, 2009; Government 
of Canada, 2010b).   
 
Food Contact Surface: 
 
A food contact surface (FCS) is any surface or ob ject that comes into contact with the RTE 
product (CFIA, 2009b).    
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 Hazard Analysis Critical Control Point (HACCP):   
 
A system that identifies, evaluates and controls hazards that are signific ant for food safety (CAC, 
2009b). 
 
Health risk categories: 
 
Health Risk 1 : 
The health risk identified represents a situation where there is a reasonable probability that the 
consumption/exposure to a food will lead to adve rse health consequences which are serious or 
life-threatening, or that the pr obability of a foodborne outbrea k situation is considered high. 
 Health Canada Advice
:  
Appropriate actions should be taken immediately to prevent e xposure of the population to the 
product, including product at the consumer level.  Follow-up acti on should try to determine the 
cause of the problem, and determine if appropria te and timely corrective measures have been 
taken.   Health Risk 2
: 
The health risk identified represents a situation where there is a reasonable probability that the consumption/exposure to a food will lead to  temporary or non-lif e threatening health 
consequences, or that the probability of serious adverse consequences is considered remote.  
 Health Canada Advice
:  
Appropriate actions should be taken in a timely manner to prevent exposure of the population to 
the product or to prevent further distribution of the product.  Follow- up action should try to 
determine the cause of the problem and determin e if appropriate and timely corrective measures 
have been taken.   
Implicated RTE products: 
   
As a minimum, all the products processed on the same line (i.e., using the same equipment) as 
the tested products are considered implicated when a tested lot has an unsa tisfactory result.  It 
should be noted that results from root cause an alysis may also trigger the need to include 
additional products as part of the implicated products.   
Line: 
 
A number of pieces of equipment (e.g., slicers, ta bles, conveyors, packaging or filling machines) 
used in series in the post-leth ality environment, as applicable , to prepare RTE foods for final 
packaging.  
 
Lot:    
 
A lot consists of all of the same product type processed on a given line, between two complete 
sanitation cycles but not exceeding one day’s pro duction.  When testing this lot, the 5 sample 
units submitted for analysis must be representative of these products and production conditions.   
  
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                                                 Novel food/process: 
 
The Food Directorate, Health Canada, has a legisl ated responsibility for pre-market assessment 
of novel foods and novel food ingredients as detailed in the Food and Drug Regulations  
(Division 28).  As per B.28.001, a “novel food” incl udes, but is not limited to: a food that has 
been manufactured, prepared, preserved or packaged  by a process that (i) has not been previously 
applied to that food, and (ii) causes the food to undergo a major change, the major change being, 
in respect to the food, a change that places the food outside the accepted limits of natural 
variations for that food, with regard to microbiological and chemical safety (Government of Canada, 2010b).  
Persistent:   
 
Repetitive FCS environmental test fa ilures, e.g., two positive results for Listeria  spp. from the 
same production line (i.e., using the same equi pment) in the RTE plan t environment within a 
short timeframe.  
 Ready-to-eat food:  
 
Ready-to-eat (RTE) foods are f oods not requiring any further pr eparation before consumption, 
except perhaps washing/rinsing, thawing or warming. 
    However, only the following kinds of RTE f oods are subject to the provisions of the Listeria 
policy: foods which have been subjected to some  form of processing in order to render them 
RTE (most often cooking) and/or which have been  subjected to another process to extend their 
shelf-life, including but not  restricted to the use of heat, chem icals, reduction of pH, reduction of 
water activity, or special packaging.  Fresh produce processed and sold as RTE are also 
included
5.  These foods may be shelf stable or may require refrigeration or freezing in order to 
assure their preservation until the time of consumption. 
 Under this definition, products such as dry goods (e .g., cereals, dried herbs,  dried spice mixtures, 
dry pasta, bread, etc.), ra w fruits and raw vegetables
6, any raw meat or raw fish or seafood7, 
 
5  RTE fresh-cut fruits and vegetables are subject to the provisions of this policy, i.e., raw fresh fruit and 
vegetables that have been either washed and peeled , either sliced, chopped or shredded prior to being 
packaged for sale and are intended to be consumed  raw and not for further processing or cooking.  
Examples include: shredded bagged lettuce, co leslaw, fresh-cut melons or fruit salad.  
6  Non RTE fresh-cut fruits and vegetables are not subject to the provisions of this policy, i.e., raw fresh 
fruit and vegetables that have been either washed, peeled, sliced, chopped or shredded prior to being 
packaged for sale with cooking instructions on the package (e.g., mixed fresh-cut vegetables intended as 
pizza dressing or intended for use in preparing soup) , as well as raw whole fresh fruits and vegetables, 
i.e., whole fresh fruit and vegetables that have only been trimmed, cleaned, brushed, washed, graded, 
packaged or otherwise prepared for human consumpti on (e.g.,  fresh herbs, whole or trimmed fruit or 
vegetables, whole leaf vegetables and berries). 
7  Exception: Sushi, which may or may not contain ra w fish, is considered a RTE food and hence is 
subject to the provisions of this policy.  
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                                                 products that are fully cooked in a hermetically -sealed container and are not exposed to the 
environment after a validated heat treatmen t, e.g., canned foods, aseptic processing and 
packaging, as well as cook-in-bag products which achieve a minimum 5-log reduction in 
numbers of L. monocytogenes , are excluded from the Listeria policy.  Processed products which 
require cooking and which are clearly labelled with adequate cooking instructions, are also 
excluded from the Listeria  policy8.   
 
Ready-to-eat foods in which growth of Listeria monocytogenes can occur (i.e., Category 1 
and Category 2A):  
 
Foods in which the growth of  L. monocytogenes can occur and the Category which the RTE food 
would fall into, would be determined based on sc ientific information.  For the purpose of this 
policy, the growth of  L. monocytogenes can occur in a RTE food if: 
 
i)  in a naturally-contaminated lot, the RTE food, throughout its st ated shelf life (e.g., durable life 
date shown as a “best before” date on the p ackage), which has been stored under reasonably 
foreseeable conditions of distribu tion, storage and use, contains L. monocytogenes  that: 
 
 - can be detected at  levels > 100 CFU/g, as determined  by direct plating (i.e.,  for 
example, MFLP-74 (see Appendix E), or any method published in the Health Canada’s Compendium of Anal ytical Methods for L. monocytogenes  in which the “application” 
section is appropriate for the intende d purpose (e.g., MFHPB-methods and MFLP-
methods)) (Category 1);  
 OR  ii)  in a representative inoc ulated batch, the RTE food, thr oughout its stated shelf life (e.g., 
durable life date shown as a “b est before” date on the package), which has been stored under 
reasonably foreseeable conditions of di stribution, storage and use, contains L. monocytogenes  
that can, as determined by the direct plating method:   
 
 -  increase in number by at least 0.5 log CFU/g9  
   AND   -  increase in number to leve ls greater than 100 CFU/g  
 (Category 1)  OR   
 
8   Processed products which have a cooked appearance  (but are not fully cooked) may be considered 
RTE, and thus may be subjected to the provisions of  this policy, if they only have microwave cooking 
instructions, or if the instructions are only to warm and serve.  
 
9  0.5 log is two times the estimated standard deviati on (i.e., 0.25 log) associated with the experimental 
enumeration viable counti ng/plate counts (CAC, 2009a).   
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   32 
 iii) in a representativ e inoculated batch, the RTE food, th roughout its stated shelf life (e.g., 
durable life date shown as a “b est before” date on the package), which has been stored under 
reasonably foreseeable conditions of di stribution, storage and use, contains L. monocytogenes  
that can, as determined by the direct plating method:     
 
 -  increase in number by at least 0.5 log CFU/g9  
     AND 
 -  increase in number to levels ≤  100 CFU/g  
 (Category 2A)  Growth of L. monocytogenes is assumed to  occur in RTE foods if the pH and a
w values fall 
outside the range specified in the notes incl uded in Table 1, i.e., pH < 4.4, regardless of a w; aw < 
0.92, regardless of pH; a combinati on of factors (e.g., pH < 5.0 and a w < 0.94) etc., unless the 
RTE food processor/importer is able  to present data, to be revi ewed by regulatory authorities 
which demonstrates that the growth of L. monocytogenes will not occur, as determined by 
validated data, in the product which has been stored under reasonably foreseeable conditions of 
distribution, storage and use through out its stated shelf-life, e.g., durable life date shown as a 
“best before” date on the package (CAC, 2009a).  Additionally, predictiv e models that are 
validated, robust and built upon scien tifically sound data can play an important role (along with 
other supporting information), in determining if  a given product formulation or process will 
reduce the likelihood of Listeria presence or growth. 
 
Ready-to-eat foods in which growth of Listeria monocytogenes will not occur as determined 
by validated methods (i.e., Category 2B): 
 
Foods in which growth of  L. monocytogenes will not occur should be determined based on 
scientific validated data and those are to be revi ewed by regulatory authorities.  Factors such as 
pH, a w, inhibitors and storage temperature, are impor tant parameters affec ting the growth of the 
organism.  Growth of L. monocytogenes is assumed not to  occur in RTE foods if the pH and a w 
values fall within the range specified in the notes included in Table 1, i.e., pH  < 4.4, regardless of 
aw; aw < 0.92, regardless of pH; a combinati on of factors (e.g., pH < 5.0 and a w < 0.94); and 
frozen foods, etc., under reasonably foreseeable conditions of distri bution, storage and use 
throughout its stated shelf-life, e.g., durable life date shown as a “best before” date on the 
package (CAC, 2009a).    
 If the physico-chemical paramete rs of a RTE food do not consis tently fall with in the ranges 
specified above, challenge test studies involving  designing, implementing and interpreting results 
would be required (Health Canada, 2010f ).  For example, the growth of L. monocytogenes can be 
controlled in RTE foods containi ng preservatives that act as antibacterial agents (e.g., food 
additives such as potassium lactate, sodium acetate, sodium diacetate, sodium lactate).  
Demonstration of no growth can be determined, for example, by experiments with naturally-contaminated food, challenge tests, information from  the scientific literatu re, validated predictive 
microbiological modeling complemented with othe r data sources, HRAs or a combination of  
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Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   33 
                                                 these10.  The demonstration of no growth should take into account the measurement error of the 
validation method.  For practical purposes, a food in which L. monocytogenes does not increase 
in numbers by 0.5 log CFU/g11 during the expected shelf-li fe under reasonably foreseeable 
conditions of distribution, storag e and use, as determined by a direct plating method (i.e., for 
example, MFLP-74 (see Appendix E), or any method published in the Health Canada’s 
Compendium of Anal ytical Methods for L. monocytogenes  in which the “application” section is 
appropriate for the intended purpose (e.g., MFHPB-methods and MFLP-methods)),  is 
considered not to support growth of the organism (CAC, 2009a).  If information is insufficient, 
inadequate or no information exists to demonstrate that there is no growth of L. monocytogenes  
throughout the shelf-life, as determined by validated  data, the food will be treated, by default, as 
a RTE food in which growth of  L. monocytogenes can occur (i.e., Category 1).  Hence, the 
sampling plan and method of analysis for Category 1 foods, as specified in Table 1, will be applied.  If questions arise, it is  the responsibility of the proce ssor/importer to demonstrate what 
category the RTE food belongs to.  
Refrigeration: 
 
Section B.27.001 of Division 27, Part B (Foods) of the Food and Drugs Regulations  defines 
"refrigeration" as follows:  “Refrigeration means exposure to a temperature of 4oC or less, but 
does not mean frozen” (réfrigéré) (Government of Canada, 2010b). 
 
10  For example, it has been demonstrated th at shredded/sliced carrots may have anti- Listeria  activity 
(Beuchat and Brackett, 1990; Nguyen-the and Lund, 1991). 
 
11  0.5 log is two times the estimated standard deviati on (i.e., 0.25 log) associated with the experimental 
enumeration viable counting/ plate counts (CAC, 2009a). 
  
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 Appendix B: Major Reported Foodborne Listeriosis Outbreaks: 
  
Table 2: Listeriosis Outbreaks Rela ted to Meat and Poultry Products  
 
Year  Location  Invasive/ 
Non-invasive Number of 
cases (deaths)  Foods  References  
1987-
1989 United 
Kingdom 
and Ireland Invasive 355 (94) Pâté McLauchlin et al. , 1991; 
Farber and Peterkin, 2000 
1990 Australia Invasive 11(6) Pâté Watson and Ott, 1990;  
Kittson, 1992 
1992 France Invasive 279 (85)  Jellied pork tongue Goulet et al. , 1993;  
Jacquet et al. , 1995;  
Salvat et al. , 1995 
1993 France Invasive 39 (12) Pork rillettes  
(pâté-like RTE 
meat) Goulet, 1995;  Goulet et 
al., 1998 
1998-1999 U.S.A. Invasive 108 (14)  Meat frankfurters Anonymous, 1998;  
Anonymous, 1999a;  Mead et al. , 2006 
1999 U.S.A. Invasive 11 Pâté Anonymous, 1999b 
1999-2000 France Invasive 10 (3) Rillettes (pâté-like 
RTE meat) de Valk et al. , 2001;  
Swaminathan et al. , 
2007 
1999-2000 France Invasive 32 (10) Jellied pork tongue Dorozynski, 2000;  de 
Valk et al. , 2001;  
Swaminathan et al. , 
2007 
2000 U.S.A. Invasive 30 (7)  Deli turkey meat Hurd et al. , 2000;  Olsen 
et al. , 2005 
2000 Australia Non-invasive 31 RTE corned beef 
and ham Sim et al. , 2002 
2001 U.S.A. Non-invasive 16 Precooked sliced 
turkey Frye et al. , 2002 
2002 U.S.A. Invasive 54 (8) Sliceable turkey 
deli-meats Anonymous, 2002;  Gottlieb et al. , 2006 
2008 Canada Invasive 57 (23)  RTE deli-meats PHAC, 2009d; PHAC, 
2010  
 
  
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 Table 3: Listeriosis Outbreaks  Related to Dairy Products 
 
Year  Location  Invasive/ 
Non-invasive Number of 
cases (deaths)  Foods  References  
1983 U.S.A. Invasive 49 (14) Pasteurized milk Fleming et al. , 1985 
1983-
1987 Switzer-land Invasive 122 (31) Soft cheese Bille, 1990; Büla  et al. , 
1995; Farber and Peterkin, 1991 
1985 U.S.A. Invasive 142 (48) Mexican-style fresh 
cheese Anonymous, 1985; Linnan et al. , 1988 
1989-
1990 Denmark Invasive 26 (6) Blue mould cheese 
or hard cheese Jensen et al. , 1994 
1994 U.S.A. Invasive 45 Chocolate milk Proctor et al. , 1995; 
Dalton et al. , 1997 
1995 France Invasive 37 (11) Raw milk soft 
cheese Goulet et al. , 1995; 
Rocourt et al. , 1997; 
Lundén et al. , 2004 
1997 France Invasive 14 Soft cheeses Jacquet et al. , 1998 
1998-
1999 Finland Invasive 25 (6) Butter made from 
pasteurized milk Lyytikäinen et al. , 2000 
2000 Canada 
(MB) Invasive 7 Flat whipping 
cream Pagotto et al. , 2006; 
Clark et al., 2010  
2000-
2001 U.S.A. Invasive 13 Mexican-style fresh 
cheese Boggs et al. , 2001; 
MacDonald et al. , 2005 
2001 Sweden Non-invasive > 120 Fresh cheese made 
from raw milk in a 
summer farm Carrique-Mas et al. , 
2003; Danielsson-Tham et al. , 2004 
2001 Japan Non-invasive 38 Washed-type cheese Makino et al. , 2005 
2001 Belgium Invasive 2 Frozen ice cream 
cake Yde and Genicot, 2004 
2002 Canada 
(BC) Invasive 47 Cheese  Pagotto et al. , 2006 
2002 Canada 
(PQ) Invasive 17 Soft and semi-hard 
raw milk cheese Gaulin et al. , 2003; 
Pagotto et al. , 2006 
2002 Canada 
(BC) Non-invasive 86 Cheese made from 
pasteurized milk Pagotto et al. , 2006 
2003 U.S.A. Invasive 13 (2)  Mexican-style fresh 
cheese Carriedo, 2003; 
Swaminathan and 
Gerner-Smidt, 2007  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   36 
 Year  Location  Invasive/ 
Non-invasive Number of 
cases (deaths)  Foods  References  
2005 Switzer-
land Invasive 10 (3)  Soft cheese Bille et al. , 2006 
2007 U.S.A. Invasive 5 (3) Pasteurized 
flavoured and non-
flavoured milk Cuming et al. , 2008 
2008 Canada 
(PQ) Invasive 38 (2) Cheeses MSSS, 2009 
2009-
2010 Austria,  
Germany and Czech Republic Invasive 34 (8) Acid curd cheese 
“Quargel” Fretz et al., 2010a;  
Fretz et al., 2010b  
 
 
 
Table 4: Listeriosis Outbreaks Rela ted to Fish and Seafood Products 
 
Year  Location  Invasive/ 
Non-invasive Number of 
cases (deaths)  Foods  References  
1989 U.S.A. Non-invasive 9 (1) Shrimp Riedo et al., 1994 
1991 Australia 
(Tasmania) Non-invasive 4 New Zealand 
produced smoked 
mussels Mitchell, 1991;  
Misrachi et al., 1991;  
Brett et al., 1998 
1992 New 
Zealand Invasive 4 (2) Smoked mussels Baker et al., 1993;  Brett 
et al., 1998 
1994-
1995 Sweden Invasive 6 (1)  “Gravad” rainbow trout and cold-
smoked rainbow 
trout Ericsson et al., 1997 
1996 Canada Invasive 2 Imitation crab meatFarber et al., 2000 
Un-
known Finland Non-invasive 5 Cold-smoked 
rainbow trout Miettinen et al., 1999 
 
 
  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   37 
 Table 5: Listeriosis Outbreaks Relate d to Fruit and Vegetable Products 
 
Year  Location  Invasive/ 
Non-invasive Number of 
cases (deaths)  Foods  References  
1981 Canada Invasive 41 (17) Coleslaw mix Schlech et al., 1983 
1997 Italy Non-invasive 1566 Corn and tuna salad Aureli et al., 2000 
1998-
1999 Australia Invasive 6 (5) Commercially 
prepared fruit salad Rooney and Sutherland, 
2001;  Abelson et al., 
2006 
 
 
Table 6: Listeriosis Outbreaks Re lated to Other Food Products 
 
Year  Location  Invasive/ 
Non-invasive Number of 
cases (deaths)  Foods  References  
1993 Italy Non-invasive 23 Rice salad Salamina et al., 1996; 
Farber and Peterkin, 
2000 
2003 United 
Kingdom Invasive 5 Prepacked 
sandwiches Dawson et al., 2006 
2009 Australia unknown 8 Chicken wrap International Food 
Safety Authorities Network, 2009 
 
    
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   38 
                                                 Appendix C: Use of Food Additi ves, Processing Aids and/or Post-Lethality Treatments for 
Ready-to-Eat Foods 
 
RTE foods exposed to the envir onment after their manufacturing pr ocess are at greater risk of 
becoming contaminated by L. monocytogenes .   Recently, new RTE product formulations that 
incorporate Listeria  inhibitors to reduce or eliminate the potential for listerial growth have been 
developed.  Alternatively, post-lethality treatments, as applicable, can also be used to reduce or 
eliminate  L. monocytogenes in RTE foods.  Although voluntary, the use of food additives, 
processing aids and/or post-lethality treatments for L.  monocytogenes in RTE foods, alone or in 
combination, is strongly encouraged for this pur pose.  In fact, since 2002 with the widespread 
use of inhibitors and robust environmental testi ng protocols, there has not been any listeriosis 
RTE meat-related outbreak in the U.S.  It re mains the responsibility  of the industry to 
demonstrate its ability and willingness to reduce the potential risks associated with RTE foods.  
It should, however, be noted that only food add itives permitted for use in Canada can be added 
and/or applied to RTE foods, as per the Food and Drugs Act and Regulations  (Government of 
Canada, 2010a and b).    
i) Food additives and/or processing aids: 
 
The use of Listeria  inhibitors (classified ei ther as food additives or processing aids under the 
Food and Drugs Act and Regulations ) is one of various steps in the overall approach to minimize 
the risks associated with L. monocytogenes in RTE foods.  During RTE food production, the 
correct implementation of GMPs will help to prevent the introduction of microbial pathogens 
and minimize their potential growth.  The function of an antimicrobial  treatment is to partially or 
totally destroy L. monocytogenes  or inhibit its growth.  Food pro cessors should be aware that the 
degree of control in thes e two areas has a signif icant impact on the overall safety of their RTE 
foods.  For this reason, the application of any liste ricidal/listeriostatic trea tment that is intended 
to be used should be validated to ensure its effectiveness and consistency (CAC, 2009a).  The 
scientific literature proposes different antimicrobial treatments for RTE foods which can achieve 
different levels of L. monocytogenes  growth inhibition and/or pathogen reduction and, therefore 
minimize the risks associated with these types of  products.  Intense resear ch is on-going to find 
effective Listeria  inhibitors that can provi de growth inhibition and/ or reduction in RTE foods 
throughout their shelf-lives.  Examples of such inhibitors include pota ssium lactate, sodium 
acetate, sodium diacetate and sodium lactate.  For practical purposes, a food in which L. 
monocytogenes does not increase in numbers by 0.5 log CFU/g12 during the expected shelf-life 
under reasonably foreseeable conditions of dist ribution, storage and use, as determined by a 
direct plating method, e.g., MFLP -74 (see Appendix E), or any method published in the Health 
Canada’s Compendium of Analytical Methods for L. monocytogenes  in which the “application” 
section is appropriate for th e intended purpose (e.g., MFHPB-methods and MFLP-methods), is 
considered not to support growth of the organism (CAC, 2009a).  The additional use of Listeria  
inhibitors in RTE foods may be re viewed by regulatory authorities, if sufficient data is provided.  
If information is insufficient, inadequate or no information exists to demonstrate that there is 
 
12   0.5 log is two times the estimated standard deviation (i.e., 0.25 log) associated with the experimental 
enumeration viable counting/ plate counts (CAC, 2009a).  
Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Bureau of Microbial Hazards, Food Directorat e, Health Products and Food Branch   39 
 ch to 
                                                limited or no growth of L. monocytogenes  (i.e., Category 2A or 2B RTE food for domestic or 
imported RTE foods) throughout the shelf-life, the food will be treated, by default, as a RTE 
food in which growth of  L. monocytogenes can occur (i.e., Category 1).  Hence, the sampling 
plan and method of analysis for Category 1 foods, as specified in Table 1, will be applied.  If 
questions arise, it is the respons ibility of the processor/importer to demonstrate what category the 
RTE food belongs to.  Currently approved food add itives that can be used to potentially control 
the growth of L. monocytogenes in foods can be found on the H ealth Canada Website (Health 
Canada, 2010g).   
 
ii) Post-lethality treatments: 
 
The use of a post-lethality treatment13 (either classified as " novel" or "non-novel" under the 
Food and Drugs Act and Regulations ), as applicable, can also be part of an overall approa
minimize the risks associated with L. monocytogenes in RTE foods.  Such an intervention step 
can reduce the levels  or inactivate any L. monocytogenes found on the surface of products due to 
post-lethality contamination.  Examples of pos t-lethality treatments include surface heat 
pasteurization (by steam, hot water, radiant ov en heating or infrared  technology) and high-
pressure processing.  At the pr esent time, a post-lethality trea tment for RTE foods that can 
achieve a minimum 3-log reduction in numbers of L. monocytogenes is recommended.  It is 
important to note that independent of the effectiv eness of the post-lethality treatment, RTE foods 
should be manufactured according to Good Ma nufacturing/Hygienic Practices (Houben and 
Eckenhausen, 2006; Huang and Sites, 2008).  A currently approved post-leth ality treatment that 
can be used to mitigate the risk of L. monocytogenes in RTE foods can be found on the Health 
Canada Website (Health Canada, 2010g).   
  
iii) Conclusion: 
 
In conclusion, the use of a combination of met hods, including an antimicrobial treatment and/or 
a post-lethality treatment, as applicable, is recommended to produce a safer RTE product.  It 
should be noted that if both strategies are used  in conjunction, a synergis tic effect could also 
potentially be achieved.    
 
13 The use of novel technologies for post-lethality tr eatments could be subjected to a comprehensive 
assessment by the Food Directorate, Health Cana da according to the Guidelines for the Safety 
Assessment of Novel Foods (Health Canada, 2006).   
 
For “non-novel” post-lethality treatments, it is hi ghly recommended that the microbiological safety and 
efficacy of these new or improved food processing and handling techniques proposed by the food industry 
(e.g., steam pasteurization, hot water treatment, radiant oven heating, infrared heating) be assessed by the 
BMH, Food Directorate, HPFB, Health Canada. Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
   
Appendix D  
 
NOTE:  This method w ill replace MFHPB-30, dated January 2001, the Supplement to 
MFHPB-30, dated March 2002, and Appendix L (Supplement to All Listeria  Methods), 
dated August 2005  in the Health Canada’s Compendium of Analytical Methods when this 
document (i.e., “Policy on Listeria monocytogenes  in ready-to-eat foods”) becomes effective.  
Also note that this Appendix will be removed and the method below will officially be moved 
to the Health Canada’s Compendium of  Analytical Methods at that time. 
 
HPB Method:                                                                                                               MFHPB -30 
  
Health Products and Food Branch 
 
Ottawa 
 
Isolation of Listeria monocytogenes  from Food and Environmental Samples 
 
Franco Pagotto, Karine Hébert and Jeff Farber 
 
Bureau of Microbial Hazards, 
Food Directorate, 
Health Canada, 
Postal locator: 2204E 
Ottawa, ON, KlA 0KB 
 
micro_methods_committee@hc-sc.gc.ca 
 
 
1. Application  
 
The method is applicable to  the detection of viable Listeria  species in foods and 
environmental samples to determine compliance with the requirements  of Sections 4 and 
7 of the Food and Drugs Act and the Policy on Listeria monocytogenes in Ready-to-Eat 
Foods (8.2). 
 
This revised method will replace MFHPB- 30, dated January 2001, the Supplement to 
MFHPB-30, dated March 2002, and Appendix L (Supplement to All Listeria  Methods), 
dated August 2005 in the  Health Canada’s  Compendium of Analytical Methods. 
  
     
2. Principle 
 
This method determines the presence of viable  Listeria species in food and environmental 
samples.  A portion of the product (or environmental sample such as a sponge or swab) is 
enriched first in a primary broth, then in a secondary en richment broth, plated onto a 
specified agar medium and one additional plating medium, and then incubated under 
specified conditions of time and temperature.  It is assumed that viable Listeria  cells will  
 
 multiply under these conditions and give rise to  visible colonies which can be identified.  
This method is based on those of Lovett ( 8.4, 8.5), Hitchins (8.3) and McClain and Lee 
(8.6), that have been modified on the basis of data collected in comparative studies by 
Warburton et al. (8.13, 8.14, 8.15).  It was revised by the addition of modified Fraser 
broth (8.7), lithium chloride-phenyletha nol-moxalactam medium (8.6), and Oxford 
(8.13), modified Oxford (8.7), and/or PALC AM (8.15) agars.  Further revisions to 
include other chromogenic media have also been made.  A mandatory step has been 
added that requires 24 h enriched LEB (UVM1 formulation) brot h to be directly streaked 
to selective agars, in addition to a tr ansfer step to modified Fraser broth. 
 
 
3. Definition of terms 
 
See Appendix A of Volume 2 of the Health Canada’s Compendium of Analytical 
Methods. 
  
4. Collection of samples 
 
4.1 See Appendix B of Volume 2 of the Hea lth Canada’s Compendium of Analytical 
Methods. 
  
4.2 For environmental samples, refer to the sampling procedures given in MFLP-41 
of the Health Canada’s Compe ndium of Analyt ical Methods. 
 
 
5.   Materials and special equipment  
 
Note: The Laboratory Supervisor must ensure that the analysis described in this method is 
carried out in accordance with the International Standard referred to as “ISO/IEC 
17025:2005 (or latest version): General Requirements for the Competence of Testing and Calibration Laboratories". 
 
The media and reagents listed below that are commercially available and are to be used, 
prepared and/or sterilized acco rding to the manufacturer's instructions. See Appendix G 
of Volume 2 of the Health Canada’s Compe ndium of Analytical Methods for the media 
formula. 
 
Note:  If the analyst uses any variations of th e media listed here (either product that is 
commercially available or made from scratch), it is the responsibility  of the analyst or 
Laboratory Supervisor to ensu re equivalency.   Please forw ard equivalency data to the 
Editor of  Compendium of Analytical Methods for consideration to modification of this 
method. 
  
 
  Listeria  broths and agars  (base media and supplements are commercially available)  
 
 1) Listeria  enrichment broth (LEB) - UVM1 formulation 
 
 2) Modified Fraser broth (MFB)   3) Oxford agar (OXA) - mandatory plating media   4) Plating media for second selective agar (one of the following is mandatory) 
 - Agar Listeria according to Ottaviana and Agosti (ALOA) 
- A.L.  Agar (Bio-Rad) - BBL CHROMagar Listeria (BD) 
   - Chromogeneic Listeria  Agar Plate (OCLA; Oxoid) 
   - Lithium chloride-phenylethanol-moxalactam medium (LPM) 
- Modified Oxford agar (MOX) - PALCAM agar (PAL) - RAPID’L.Mono (Bio-Rad) 
    
5) Control cultures (use ATCC strains or equivalent) 
Positive controls: Listeria  monocytogenes,  Listeria ivanovii , Listeria innocua , 
Listeria grayi (Staphylococcus aureus  and Rhodococcus equi  - optional) 
             
6) Stomacher, blender or equivalent, vortex mixer 
  7) Microscope  
8)        Incubators capable of maintaining 30
oC and 35oC 
 
Note:   It is the responsibility of each laboratory to ensure that th e temperature of the incubators 
or water baths is maintained at the recommended temperatures.  Where 35°C is 
recommended in the text of the method, the incubator may be at 35 +/-1.0° C.  Similarly, 
lower temperatures of 30 or 25°C may be  +/- 1.0°C.  However, where higher 
temperatures are recommended, such as 43 or 45.5°C, it is imperative that the incubators 
or water baths be maintained within 0.5°C due to potential lethality of higher 
temperatures on the microorganism being isolated.  
 
 Confirmation Media and Reagents  
 
 9)  Tryptose broth and agar (TA)   10) Trypticase soy broth and agar, with 0.6% yeast extract (TSB-YE and TSA-YE) 
  11) Horse or sheep blood agar (recommended for hemolysis test)   12) Motility test medium   
 13) Carbohydrate fermentation agars or brot hs (mannitol, rhamnose and xylose).  
    Note : these biochemicals may be done vi a rapid identification kits (6.8.2) 
    
Optional  
 
 14) Rapid identification kits, such as the Vitek or API Listeria  (Bio Mérieux Vitek, 
Inc.), Micro-ID Listeria  (Organon Teknika Corp.), the Listeria  AccuprobeTM Test 
(Gen-Probe; MFLP-88) or Oxoid Biochemi cal Identification System (O.B.I.S.) 
Mono kit (Oxoid) or equivalent 
 
15) Other Chromogenic or nove l agar - novel chromogenic and other isolation agars 
may be used, but only in conjunction with the plating media that are mandatory in 
the method. 
 
16) Sheep blood agar - for CAMP test 
  17) Latex Agglutination kit (e.g., Oxoid Listeria  Test Kit) 
 
18) Listeria  monocytogenes antisera (e.g., Denka Seiken) 
  
19) Gram stain solutions   20)       3% hydrogen per oxide (for the catalase test) 
 
21) Biochemicals - dextrose, esculin, maltose, α-methyl-D-mannoside 
  22)       Beta-lysine discs (e.g., Remel)   
6. Procedure  
 
Each sample unit may be analysed individually  or the analytical units may be composited 
according to the sampling scheme describe in the Listeria  Policy.  Maintain a ratio of 1 
part sample material to 9 parts steril e enrichment broth. Information regarding Listeria  
distribution can be obtained by analysing each analytical unit separately.  Carry out the 
test in accordance with the following instructions: 
 
6.1 Handling of Sample Units  
 
       6.1.1 In the laboratory prior to an alysis, except for shelf-stable foods, keep 
sample units refrigerated or fro zen, depending on the nature of the 
product. Thaw frozen samples in a refrigerator, or under time and 
temperature conditions which prev ent microbial growth or death. 
 
       6.1.2 Analyze sample units as soon as possible after their receipt in the 
laboratory.   
  
 6.2 Preparation for Analysis 
 
        6.2.1 Have sterile Listeria  enrichment broth (LEB) ready, pre-warmed to 30 +/- 
1 oC before use. 
 
  6.2.2 Clean the surface of the working area with disinfectant. 
 
6.3 Preparation of Sample  
 
To ensure a representative analytical unit,  agitate liquids or free flowing materials 
until the contents are homogeneous. If the sample unit is a solid, obtain the 
analytical unit by taking a portion from se veral locations within the sample unit. 
 
6.4 Enrichment Procedure (see Figure 4) 
 
Note :  To allow flexibility for incubation times stated, the following guidelines can 
be used. Incubation times of 24 h are +/- 2h; incubation times of 48 h are +/- 
4 h.  
 
Environmental Samples : Add the environmental sponge  or large swabs to 100 mL 
of LEB or composite up to 10 sponges with 100 mL LEB per sponge (see MFLP-
41 of the Health Canada’s Compendium of Analytical Met hods).  Place smaller 
environmental swabs (e.g., co tton tip) in 10 mL portions of LEB or composite up 
to 10 swabs with 10 mL LEB per swab. 
 Food Samples: Add 25 g or mL of the food (the analytical unit) to 225 mL of LEB in a blender jar or stomacher bag.  For composite samples, analytical units 
may be combined up to 125 g or ml (e .g., 125 g or mL of food to 1125 mL of 
LEB).   If alternate analytical units are re quired, maintain a ratio of 1 part sample 
material to 9 parts LEB. 
 
For both environmental samples and food blend, stomach or vortex as required 
for thorough mixing. LEB culture may be in cubated in the stomacher bag or other 
sterile container.  Incubate  LEB culture for 48 h at 30
oC. 
           6.4.1 Refrigeration of inc ubated enrichment broth (LEB)  - OPTIONAL 
  
   6.4.1.1 This approach allows for the refrigeration of incubated broth for up 
to 4 days and provides greater flexibility. 
     6.4.1.2  Mix thoroughly after refriger ation before proceeding with 6.5.   
 
6.5 Selective Enrichment  
 
 6.5.1 At 24 and 48 h, mix the LEB cultu re by swirling or vortexing, and 
inoculate 10 mL of modified Fraser  Broth (MFB) with 0.1 mL of the LEB  
 culture. Incubate 24-26 h at 35oC.   In addition, at 24 h (at the same time 
that the transfer is made from LEB  to MFB), proceed with Step 6.6 by 
directly streaking to the selective agars as describe d in 6.6.1.  It is optional 
to streak 48 h LEB enrichment to selective plates. 
 
Helpful hint:   Vortex the MFB at 20 to 24 h, then reincubate for an additional 2 to 6 h 
before reading reaction.  Reading the MFB at 26 h can substantially 
reduce the plating done at 48 h. 
    6.5.2 Streak MFB onto plates if positiv e.  A positive broth has darkened and 
may be black, dark brown or dark green.  A negative MFB has the straw colour of a newly made broth.  If negative, reincubate another 24 h and streak all positive broth.  Proceed with Step 6.6. 
  
 6.6  Isolation Procedure 
 
 6.6.1 After vortexing, streak positive MF B onto two different plating media. 
Use Oxford agar and one of the follo wing agars as listed in Section 5:  
ALOA formulation agar, A.L.  Agar, BBL CHROMagar Listeria, 
Chromogeneic Listeria Agar Plate,  lithium chloride-phenylethanol-
moxalactam medium, modified Ox ford agar, PALCAM agar, or 
RAPID’L.Mono.  Incubate LPM plates at 30oC and all other selective 
agars at 35oC for 48 h, examining all plates at 24 h for typical colonies, 
unless otherwise directed by the manufacturer.  Note that there are up to 2 plates pr oduced for each selective agar (one 
from the streaking of 24 h LEB enriched broth which will always be present and potentially one from positive MFB tube).  
 
 6.6.2 OXA  agars - Listeria  species form 1 mm diameter black colonies 
surrounded by black haloes after 24 h.  At 48 h colonies are 2-3 mm in 
diameter, black with a black halo an d sunken centre.  The colonies can 
also appear brown-black  or green-black.  When examined before 24 h, 
growth of Listeria  spp. is sometimes apparent but without the 
characteristic blackening.  Some strains of this genus, other than L. 
monocytogenes,  are inhibited on this medi um when incubated at 35oC. 
 
Note : One of the following media is used in conjunction with Oxford 
agar, which is mandatory in the method. 
 
   6.6.3 Agar Listeria according to Ottaviani & Agosti  - Listeria colonies 
appear blue-green, with L. monocytogenes  and L. ivanovii  colonies having 
opaque halos surrounding the colo nies after 24 h. All other Listeria 
species are blue-green but do NOT have the halo. Consult manufacturer 
insert for a more detailed description  
  
6.6.4 A.L. agar - all Listeria  spp. form blue to blue -green colonies with L. 
monocytogenes and L. ivanovii colonies having opaque halos around the 
colonies after 24 and 48 h, respectively. 
 
6.6.5 BBL CHROMagar - L. monocytogenes and L. ivanovii  are blue-green 
colonies surrounded by a opaque white halo.  Other Listeria  spp. are blue-
green colonies without a halo.  
 
6.6.6 LPM  - Examine LPM plates for suspect colonies using beamed white 
light powerful enough to illuminate th e plate well, striking the plate 
bottom at a 45o angle.  Under optimum transi llumination the more isolated 
and larger (48 h old) Listeria  colonies appear as whitish piles of crushed 
glass often showing mosaic-like internal structures occasionally having 
blue-grey  iridescence that tends to sparkle.  Alternatively, the colonies can 
look smooth with a blue tinge around the perimeter.  When growth becomes near confluent, an even blue-grey iridescent sheen can be observed . 
 6.6.7 MOX agars  - Listeria  species form 1 mm diameter black colonies 
surrounded by black haloes after 24 h.  At 48 h colonies are 2-3 mm in 
diameter, black with a black halo an d sunken centre.  The colonies can 
also appear brown-black  or green-black.  When examined before 24 h, 
growth of Listeria  spp. is sometimes apparent but without the 
characteristic blackening.  Some strains of this genus, other than L. 
monocytogenes,  are inhibited on this medi um when incubated at 35
oC. 
 
6.6.8 Brilliance Listeria A gar (formerly OCLA agar)  - L. monocytogenes and  
L. ivanovii appear as blue colonies surrounded by an opaque halo, whilst 
other Listeria species produce blue colonies without a halo after 24 h. 
  
 6.6.9 PAL agar  - Listeria  species form 2 mm grey-green colonies with a black 
sunken centre and a black halo on a cherry-red background.  Some Enterococcus  and Staphylococcus strains form grey colonies with a 
brown-green halo or yellow co lonies with a yellow halo.  
  
6.6.10 RAPID’L.Mono - L. monocytogenes  forms blue colonies without yellow 
halo while L. ivanovii  are greenish-blue colonies  with yellow halo; other 
Listeria  species are yellow to white in colour.  
 
6.7  Identification Procedure - Confirmation     
 
 6.7.1 If the colonies are well isolated on the selective agars:  Pick a minimum of 
5 typical colonies from each selective plate to blood agar (6.7.2) at each step of the method that selective pla ting is done (e.g., after 24 h LEB, after 
darkening of MFB broth etc.).   
  
If the colonies are NOT well isolated on the selective agars:   Pick a 
minimum of 5 typical colonies from each selective plate to Tryptose agar or Trypticase soy agar with 0.6% yeas t extract, streaking for separation.  
As above, pick a minimum of 5 typical colonies from each step of the method that required purification from selective agars.  In cubate plates at 
30
oC for 24-48 h or until growth is satisfactory. Examine the plates for 
typical colonies using the light  arrangement already described in 6.6.6.  
 Confirmation of Listeria  spp. can be accomplished by using motility, 
hemolysis and 3 carbohydrate agars (m annitol, rhamnose and xylose) or 
other valid confirmation steps that are published in the Compendium of 
Analytical Methods as e quivalent.  Other biochemi cal tests are optional.  
Rapid identification kits may be helpfu l to reinforce confirmation of these 
results and differentiate the different Listeria  species (see 6.8.1).  
 
 6.7.2 Hemolysis:  
 
On blood agar plates (sheep or horse ), draw a grid of 20-25 spaces on the 
plate bottom.  Pick typical colonies from the selective agars (if colonies 
are well isolated) or from the TA or TSA-YE plates (if streaked for purity) 
and inoculate the blood agars by stabbing one colony per grid.  
 
Stab positive and negative controls ( L. monocytogenes,  L. ivanovii  and L. 
innocua  or L. grayi ) on each plate.  Incubate for 24 h at 35oC. 
 
NOTE:  It is recommended that you stab blood agar plates and carbohydrate 
plates (6.7.4) concurrently from the same colony (motility agar may also be stabbed at this time). Ensure that  each colony is placed in the same 
position on all grid plates.  
 
Examine blood agar plates containing culture stabs by transillumination using a bright light (holding the plate so that the light shines through from 
the back of the plate).  L. monocytogenes produces a slight cleared zone 
around the stab; L. innocua shows no zone of hemolysis, whereas L. 
ivanovii  produces a well-defined zone of clearing around the stab.   
 
   6.7.3     Motility:  
Agar:  Stab motility test medium from selective agars, TA or TSA-YE.  
Incubate motility test media for a mini mum of 48 h at room temperature.  
Observe daily.  Only Listeria  spp. gives typical umbrella growth pattern. 
 
 and/or  
Wet mount : Pick at least one typical col ony from selective agar, TA or  
 TSA-YE that is incubated at 30° C or less, and do a wet mount 
examination using 0.85% saline for the suspending medium and the oil 
immersion objective of a phase -contrast microscope.   
 
Alternately: Inoculate TSB-YE or TB brot hs and incubate overnight at 
30oC. Transfer a loopful of the overnight cultures to a fresh TSB-YE or 
TB and incubate at 25oC for 6 hours. Put a drop of each 6 hour culture 
onto a glass slide and examine for typical Listeria motility using the oil 
immersion objective of a phase contrast microscope. Listeria appears as 
slim, short rods with tumbling motility.  Always compare to a known 
Listeria culture. Cocci, large rods, or rods with rapid swimming motility 
are not  Listeria  species . 
 
 6.7.4 Carbohydrate Utilisation:  
 
Plates:  On carbohydrate (mannitol, rham nose and xylose) agar plates, 
draw a grid of 20-25 spaces on the plat e bottom.  Pick typical colonies 
from the selective agars, TA or TS A-YE plates and inoculate agars by 
stabbing one culture per grid.  Ensure  that each colony is placed in the 
same position on all grid plates. Always stab positive and negative controls ( L. ivanovii , L. monocytogenes  and L. grayi ).   Incubate for 24 h 
at 35
oC. 
                                  and/or  
Broths:  From TSB-YE culture, inoculat e the following carbohydrates set 
up as 0.5% solutions in purple car bohydrate broth: dextrose, esculin, 
maltose, mannitol, rhamnose, α-methyl-D-mannoside and xylose. Incubate 
7 days at 35
oC.  Examine daily.  Listeria  spp. produces acid with no gas, 
or no reaction.   
 
Consult Table 7 for the ca rbohydrate reactions of the Listeria  spp. 
 
6.8  Identification Procedure - Optional Tests  
 
 6.8.1 PCR:  
 From a single colony from select ive agar, follow a validated PCR 
confirmation method for detection of  Listeria  spp. (see Health Canada’s 
Compendium of Analytical Methods).  It is suggeste d that the colonies that 
have been identified by PCR be streaked onto TSA or TSA-YE from the 
blood agar (6.7.2) to obtain isolates of positives. Biochemical assays may 
be required if mentioned in the PCR method; check the specific PCR method for guidance.  Also see the PCR method for interpretation of PCR 
results.        
   
  6.8.2 Rapid Identification Kits:  
Rapid identification kits, such as the Vitek or API Listeria , Micro-ID 
Listeria , the Listeria  AccuprobeTM Test, or equivalent can be used.  Follow 
manufacturer’s instru ctions for use.  
 
 6.8.3 Catalase: 
Test a typical colony for catalase. Transfer a colony onto a clean glass 
slide and add one drop of 3% hydrogen peroxide. Development of  bubbles  
is indicative of a positive  reaction . Listeria cells are catalase-positive. 
Avoid picking test colonies from agars containing blood as they can 
produce a false positive result. 
  
 6.8.4 Gram stain:    
      Listeria  is a small Gram-positive rod. 
 
6.8.5 CAMP test:    
For the CAMP test, streak fresh isolates of beta-hemolytic Staphylococcus 
aureus  and Rhodococcus equi  vertically on a sheep blood agar plate.  
Separate the vertical streaks so th at test strains may be streaked 
horizontally between them without touching the verti cal streaks.  After 24-
48 h incubation at 35oC, examine the plates for hemolysis in the zone of 
the vertical streaks. 
 
  6.8.5.1 The hemolysis of L. monocytogenes  and L. seeligeri  is 
enhanced in the vicinity of the Staphylococcus streak; while 
L. ivanovii  hemolysis is enhanced near the Rhodococcus 
streak.  The other Listeria  species are CAMP test negative.  
The test can differentiate L. ivanovii  from L. seeligeri , and 
a weakly-hemolytic L. seeligeri from L. welshimeri .   
         
  6.8.5.2 An alternative and convenient CAMP test may be 
performed using the S. aureus factor in commercially 
prepared sterile beta-lysine discs.   In this test, a beta-lysine 
disc is placed in the center of the sheep blood plate and 4-5 
Listeria  cultures are streaked as radiating lines from the 
disc, being careful not to touc h the disc with the inoculum. 
After 18-24 h incubation at 35oC, a very sharp CAMP 
reaction between L. monocytogenes  or L. seeligeri cultures 
and the disc can be observed.  L. ivanovii  are strongly 
hemolytic and form a clear beta hemolytic line along the 
entire streak. 
 
  6.8.6 Serology:    
     Follow manufacture's instru ctions provided with the antisera. 
    
  6.9  Interpretation of Results for Speciation 
 
Listeria spp. are small, Gram-positive motile rods that are catalase-positive, urea-
negative, and produce an acid slant a nd butt in TSI without production of H 2S.  
They utilize dextrose, esculin, and maltose, with some species also using 
mannitol, rhamnose, and xylose with pr oduction of acid.  All species give +/+ 
reactions in MR-VP broth.  L. grayi  and L. murrayi  are the only two species 
which utilize mannitol.  L. murrayi  is the only species which can reduce NO 3- to 
NO 2-. It should be noted that L. grayi and L. murrayi  are proposed to be 
considered members of a single species (8.10). 
 
L. monocytogenes , L. ivanovii , and L. seeligeri (weak) produce hemolysis in horse 
or sheep blood agar and are also positive in the CAMP test.  Of the three, only L. 
monocytogenes cannot utilize xylose, but  is rhamnose-positive.  L. ivanovii can be 
differentiated from L. seeligeri by the CAMP test, where L. seeligeri  shows 
enhanced hemolysis only at the Staphylococcus streak and L. ivanovii shows 
enhanced hemolysis in the area of the R. equi  streak. 
 
L. innocua can be differentiated from L. monocytogenes  by its lack of hemolysis 
on blood agar plates and negative reaction in the CAMP test.  L. welshimeri that is 
rhamnose-negative may be confus ed with a weakly-hemolytic L. seeligeri unless 
the CAMP test is run. 
 
All biochemical, serological, and pathogenici ty data are summarized in Tables 7 
and 8.   
 
 
7. Reporting of results 
 
A final report contains informa tion on the presence or absence of Listeria 
monocytogenes in the test portion analysed.  If other Listeria species are isolated, 
these may be noted in the test report, if agreed between the parties concerned.    
 
The final report shall also include all information necessary for the complete 
identification of the sample, the method that  was used, including any deviations in 
method, information specifying the mass in grams, or the volume in millilitres.  Any information that may have influenced the outcome of the test should be included in the final report. 
  
8. References  
 
 8.1  Bille, J. 2007.  Listeria and Erysipelothrix . In P.R. Murray (ed.), Manual of 
Clinical Microbiology, 9
th Edition. ASM Press, pp. 474-484. 
   8.2  Health Canada, Health Products and Food Branch, Food Directorate.  Policy on  
 Listeria monocytogenes  in Ready-to-Eat Foods. 
 
 8.3  Hitchins, A.D. 1995. Listeria monocytogenes. Chapter 10.  Revised 1998.  
Bacteriological Analytical Manual (BAM).   AOAC International. Gaithersburg, 
MD. 
 
 8.4  Lovett, J.  1987.  Listeria  isolation.  Chapter 29. B acteriological Analytical 
Manual (BAM). AOAC. Arlington, Virginia. 
 
8.5  Lovett, J. and A.D. Hitchins. 1988.  Listeria  isolation.  Chapter 29.  Revised 
October 13, 1988.  Bacteriological Anal ytical Manual (BAM).  AOAC.  
Arlington, Virginia. 
    
8.6  McClain, D. and  W.H. Lee. 1988.  Development of USDA-FSIS Method for 
Isolation of Listeria Monocytogenes  from Raw Meat and Poultry.  JAOAC.  
71(3):660-664. 
 
8.7  McClain, D. and W.H. Lee. 1989.  FSIS Method for the Isolation and 
Identification of Listeria Monocytogenes From Processed Meat and Poultry 
Products.  USDA-FSIS Labor atory Communication N o. 57.  Revised May 24, 
1989. 
 
8.8  McLauchlin J. 2005. Listeria . In S.P. Borriello, P.R. Murray and G. Funke (ed.), 
Topley and Wilson’s Microbiology and Microbial Infections, 10th Edition. ASM 
Press, pp. 956-969. 
 
8.9  Rocourt, J., and C. Buchrieser. 2007.  The genus Listeria and Listeria 
monocytogenes: Phylogenetic position, taxonomy and identification. In E.T. Ryser 
and E.H. Marth (ed.), Listeria , Listeriosis and Food Safety, 3rd edition. CRC 
Press, pp. 1-20.  
 8.10 Rocourt, J., P. Boerlin, F. Grimont, Ch. Jacquet, and J.-C. Piffaretti. 1992.  
Assignment of Listeria grayi and Listeria  murrayi to a single species, Listeria 
grayi, with a revised description of Listeria  grayi.  Int. J. Syst. Bacteriol 42: 69-73 
  8.11 Seeliger, H.P.R. and D. Jones.1986. The Genus Listeria . Bergey's Manual of 
Systematic Bacteriology.  Volume 2.  Williams and Wilkins, Baltimore.  pp. 
1235-1245. 
  8.12 Wagner, M. and J. McLauchlin. 2008. Biology. In D. Liu (ed.), Handbook of 
Listeria monocytogenes . CRC Press, pp. 3-25 
 
8.13 Warburton, D.W., J.M. Farber, A. Armstr ong, R. Caldeira, T. Hunt, S. Messier, R. 
Plante, N.P. Tiwari and J. Vinet. 199 1.  A Comparative Study of the "FDA" and 
"USDA" Methods for the Detection of Listeria monocytogenes  in Foods.  Int. J. 
Food Microbiol. 13( 2):105-118. 
  
  8.14 Warburton, D.W., J.M. Farber, A. Ar mstrong, R. Caldeira, N.P. Tiwari, T. 
Babiuk, P. LaCasse and S. Read. 1991.  A Canadian Comparative Study of 
Modified Versions of the "FDA" and "USDA" Methods for the Detection of 
Listeria monocytogenes .  J. Food Prot.  54(9):669-676. 
 
8.15 Warburton, D.W., J.M. Farber, C. Powell,  N.P. Tiwari, S. Read, R. Plante, T. 
Babiuk, P. Laffey, T. Kauri, P. Mayers, M.-J. Champagne, T. Hunt, P. LaCasse, 
K. Viet, R. Smando and F. Coates.  1992.  Comparison of Methods for Optimum 
Detection of Stressed and Low Levels of Listeria monocytogenes .  J. Food 
Microbiol.  9:127-145.  
   
 
Table 7:  Characteristics differen tiating the species of the genus Listeriaa 
 
Characteristic  L. monocytogenes  L. innocua  L. ivanovii subsp. 
ivanoviiL. ivanovii subsp. 
londoniensis  L. welshimeri  L. 
seeligeri  L. grayi 
Gram stain + + + + + + + 
Beta-hemolysis + - ++b ++ - + - 
Acid production from:        
     Mannitol - - - - - - + 
     L-Rhamnose + V - - V - V 
     D-Xylose - - + + + + - 
CAMP reaction        
     S. aureus  + - - - - + - 
     R. equi  V - + + - - - 
        
Acid production from:        
   α -Methyl-D-mannoside + + - - + - + 
    Soluble starch - - - - ND ND + 
    Ribose - - + - - - V 
    N-Acetyl- β-D-mannosamine ND ND V + ND ND ND 
Hippurate hydrolysis + + + + ND ND - 
Lipase production + - +  + - + - 
Arylesterase activity - + + + + + + 
Reduction of nitrate - - - - ND ND V 
 
a+, 90% of strains are positive; -, 90% of strains are negative; ND, not determined; V, variable. Adapted from 8.1, 8.8, 8.9, 8.11 and 8.12 
b++, usually a wider zone of hemolysis observed 
 
 
 
 
  
 
 
   
 Table 8:  Serology, hemolytic activity and mouse virulence for Listeria  species 
  
Species Serotype Hemolysis of  
horse blood (7%) stab Mouse virulence 
L. monocytogenes  1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4a, 4ab, 4b, 
4b(x), 4c, 4d, 4e, 7 + + 
L. ivanovii  5 + + 
L. innocua  4ab, 6a, 6b, un* - - 
L. welshimeri  6a, 6b - - 
L. seeligeri  1/2b, 4c, 4d, 6b, un* + - 
 
* un = undefined. 
 
   
 Figure 4:  A Flow Diagram Showing the Isolation Procedure  
 
 
 
 
Blend or stomach in LEB broth.  Incubate at 30oC for 48 h. 
     
           
 
  
At 24 and 48 h transfer 0.1 mL of the LEB into 10 mL MFB. Incubate up to 48 h at 35
oC. 
Streak 24 h LEB onto plates - Oxford agar, plus an additional plating media as listed above. 
  
 
  
 
 
Streak positive MFB onto selective agar plates. Reincubate negative MFB for an additional 24 h. 
Incubate plates for 48h (check plates at 24 h). 
    
 
  
 
 
 
Confirmation tests  
 
motility 
hemolysis 
mannitol, rhamnose and xylose 
(or approved Compendium method  
equivalent to these required steps) 
 
 
 
Optional tests  
 
other biochemicals 
rapid identification kits 
PCR 
catalase 
Gram stain 
serology 
 
 
 
 
  
 
 
   
 Policy on Listeria monocytogenes in Ready-to-Eat Foods 
 
 
Appendix E  
NOTE:  This method will rep lace MFLP-74, dated April 2002 ( 7.1), and the Supplement to 
MFLP-74, dated April 2004 (7.2) in the Health  Canada’s Compendium of Analytical 
Methods when this document (i.e., “Policy on Listeria monocytogenes  in ready-to-eat 
foods”) becomes effective.  Also note that this Appendix will be removed and the method 
below will officially be moved to the Health Canada’s Compendium of Analytical Methods 
at that time. 
 
Laboratory Procedure:                                                                                                   MFLP-74   
Health Products and Food Branch 
 
Ottawa 
 
Enumeration of Listeria monocytogenes  in Foods  
 
Franco Pagotto  1, Yvon-Louis Trottier  1, Jacqueline Upham  2 and Irene Iugovaz  1  
 
1 Research Division, Bureau of Microbial H azards, Food Directorate, Health Canada, Ottawa, Ontario, HPFB, Postal Locator 2204E, K 1A 0K9 
2   Canadian Food Inspection Agency, Microbiology, Dartmouth Laboratory, 1992 Agency drive, Dartmouth, NS, B3B 1Y9. 
 
 micro_methods_committee@hc-sc.gc.ca 
  
 
1. Application                    
 
This method is applicable to the enumeration of viable Listeria monocytogenes  in foods 
where quantitative determination of the levels of Listeriae  in foods is required. This 
method will replace MFLP-74, dated April 2002  (7.1), and the Supplement to MFLP-74, 
dated April 2004 (7.2). 
 
  
2. Principle 
 
This direct plating procedure quantita tively determines the number of viable  Listeria 
monocytogenes in the product.  A portion of the product is blended in a suitable diluent, 
surface-plated onto at least tw o selective agars, and the plates are then incubated under 
specified conditions of time and temperature. It is assumed that each viable cell of L. 
monocytogenes will multiply under these specified incubation conditions and give rise to a visible colony which can be identified. The selective media used are based on studies 
done by other investigators (7.3, 7.4, 7.5). 
 
 
3. Definition of terms 
 
See Appendix A of Volume 3 of the Health Canada’s Compendium of Analytical 
Methods.  
  4. Collection of samples 
 
See Appendix B of Volume 3 of the Health Canada’s Compendium of Analytical 
Methods. 
 
 
5. Materials and special equipment  
 
See MFHPB-30, ‘Materials and Special E quipment’ of the Health Canada’s 
Compendium of An alytical Methods.. 
 
 See Appendix G of the Health Canada’s Co mpendium of Analyti cal Methods (Volume 
1) for the formulas of individual media  
 
 Additional requirements: 
 
 1) Peptone water, 0.1% (w/v)   2) Plating media:    Selective media include the following: 
 
   - OXA (mandatory agar)    One of the following is to be included with OXA: 
 
- Agar Listeria according to Ottaviani & Agosti 
     - A.L. agar 
   - BBL Chromagar Listeria 
   - Brilliance Listeria Agar (formerly OCLA agar) 
   - Lithium chloride-phenylathanol-moxalactam medium (LPM) 
   - Modified Oxford agar (MOX) 
   - Palcam agar (PAL) 
   - Rapid L’Mono 
    
  
6. Procedure  
 
Information regarding the distribution of Listeria  monocytogenes can be obtained by 
testing each analytical unit separately. 
 
 6.1 Handling and Dilution of Sample Units 
 
 6.1.1 In the laboratory prior to analysis , except for shelf-stable foods, keep 
sample units refrigerated or frozen depending on the nature of the 
product.  Thaw frozen samples in the refrigerator, or under time and 
temperature conditions which prev ent microbial growth or death. 
 
  6.1.2 Analyses should be started as soon as possible after receipt of samples in 
the laboratory.  
  
  6.1.3 To ensure a representa tive analytical unit, agita te liquids or free flowing 
materials until the contents are homogeneous. If the sample unit is a solid, obtain the analytical unit by ta king a portion from several locations 
within the sample unit. The analytical sample recommended is 10 grams or 10 ml.  
   
 6.2 Direct Plating Procedure  
   6.2.1 Prepare a 1:5 dilution of the samp le, as required, in 0.1% (w/v) peptone 
water in a blender jar or stomacher bag. Blend or stomach for 2 minutes 
to ensure thorough mixing. For food matrices that require a higher 
dilution to allow for ease of spread ing the food/diluent slurry on the 
selective plates, a 1:10 dilution may be used.  This may require the 
plating of additional sample aliquot over additional plates.  
 
Two agar types are used to enumerate L. monocytogenes  as follows: 
immediately spread 1 ml by taking th ree, 0.333 mL portions of the diluted 
food, and spread onto the surface of 3 plates of each selective media (e.g., 
a total of 2 mL is plated over two ag ar types).  Selective media includes  
OXA and one of the approved agars listed in section 5. 
 
  6.2.2  Incubate LPM at 30°C and all ot her selective agars at 35°C for 48 h, 
examining all plates at 24 h for typical colonies, unless otherwise 
directed by the manufacturer .  Observe for colonies with a typical 
appearance (section 6.3.1 to 6.3.4). 
 
   
 6.3 Presumptive Identification  NOTE:   
 
1. Prior to use ensure agar plates are dry to avoi d undue spreading of colonies. After spreading a 
sample aliquot, ensure that the agar plate is dry before inverting and placing in an incubator. 
 2. If other chromogenic agar plating media and other novel isolation agar is to be used, it may be 
done, but only in conjunction with  the mandatory plating and one of the listed plating media in 
section 5. Three agar plates of each unvalidated chromogenic agar should be used as per the agars listed in section 5.  
 3. To allow flexibility for incubation times, the foll owing guidelines can be us ed: incubation times of 
24 h  +/- 2 h or 48 h for +/- 4 h. 
 
   6.3.1 OXA and MOX agars  - L. monocytogenes forms 1 mm diameter black 
colonies surrounded by black haloes af ter 24 h.  At 48 h, colonies are 2-3 
mm in diameter, black with a blac k halo and sunken centre.  The  
 colonies can also appear brown-black and green-black.  Other Listeria 
spp. shows a similar appearance.  When examined before 24 h, growth of 
Listeria  spp. is sometimes apparent but without the characteristic 
blackening.  Some strains of  this genus other than L. monocytogenes are 
inhibited on this medium when incubated at 35°C.   
   6.3.2 LPM  - Examine LPM plates for suspect colonies using beamed white 
light powerful enough to illuminate th e plate well, striking the plate 
bottom at a 45° angle (7.6).  Under optimum transillumination, the more isolated and larger (48 h old)  Listeria  spp. colonies appear as whitish 
piles of crushed glass often showi ng mosaic-like internal structures, 
occasionally having blue-grey iridescence that tends to sparkle.  Alternatively, the colonies can look smooth with a blue tinge around the 
perimeter.  When growth becomes n ear confluent, an even blue-grey 
iridescent sheen can be observed. 
   6.3.3 PAL agar  - L. monocytogenes colonies are approximately 2 mm grey-
green with a black sunken centre an d a black halo on a cherry-red 
background.  Some Enterococcus and Staphylococcus strains produce 
grey colonies with a brown-green ha lo or yellow colonies with a yellow 
halo. 
 
  6.3.4 Agar Listeria according to Ottaviani & Agosti  - Listeria colonies 
appear blue-green, with L. monocytogenes  and L. ivanovii  colonies 
having opaque halos surrounding the colonies after 24 h. All other 
Listeria species are blue-green but do NOT have the halo. Consult manufacturer insert for a more detailed description.  
 
  6.3.5 A.L. agar - All Listeria species form blue to blue-green colonies, with L. 
monocytogenes and L. ivanovii  colonies having opaque halos 
surrounding the colonies afte r 24 and 48 h, respectively. 
 
  6.3.6 BBL CHROMagar  - L. monocytogenes and L. ivanovii appear as blue-
green colonies surrounded by a opaque white halo.  Other Listeria  spp. 
are blue-green colonies without a halo. 
 
  6.3.7 Brilliance Listeria Agar (formerly OCLA agar)  - L. monocytogenes  
and L. ivanovii appear as blue colonies surrounded by an opaque halo, whilst other Listeria species produce blue coloni es without a halo after 
24 h. 
   6.3.8 Rapid L’Mono agar  - L. monocytogenes forms blue colonies without a 
yellow halo whereas L. ivanovii  are greenish-blue w ith a yellow halo.  
All other Listeria species are yellow to white in colour. 
  
  6.4 Enumeration and Confirmation of Co lonies from Direct Plating Procedure   
 
  6.4.1 Examine each set of triplicate plat es from the two selective media used, 
for typical colonies.  Because it is expected that listeriae will be present 
in low numbers, each colony must be confirmed prior to reporting of the 
results, up to 15 colonies per agar type. 
 
6.4.2 Confirm presumptive colonies as  L. monocytogenes by following the 
procedures described in MFHPB-30 (7.7, 7.8). If colonies are not well 
separated, purify up to 15 colonies per agar type by streaking onto TSA 
agar and incubating at 30 ºC for 24 or 48 hours until growth is 
satisfactory. 
 
NOTE: At minimum, all coloni es up to 15 per agar type should be confirmed prior to 
reporting of the results as described in section 6.5.  
  
   6.5 Interpretation  
   
  6.5.1 Record the results separately fo r each of the two selective agars. 
Calculate the colony forming units (CFU) per g (or ml) using the 
following equation: 
 
Number of CFU 
Volume plated (ml) x total dilution 
factor 
 
Example:  
 
A 1:5 dilution is made from a food matrix.  One (1) ml is spread onto 
three OXA plates and 1 ml is spr ead onto three PAL plates.  After 
incubation, the sum total of each OXA plate is 5 colonies and the sum 
total of the PAL plates is 15 colonies.  
 
 
  Using the above equation:   
5 colonies 
1 (volume plated, ml) x 0.2 (dilution 
factor) 
 
       = 25 CFU/g  
   Repeating with the PAL plates:  
  
 15 colonies 
1 (volume plated, ml) x 0.2 (dilution 
factor) 
 
       = 75 CFU/g 
 
  Final report = 75 CFU/g [Note that only the highest number is reported] 
   
  
 NOTE:  Whenever possible, the actual count sh ould be reported.  Other options, 
considerations or helpful hints include the following:   a:  If there are no colonies in the 1:5 dilution, report as <5 CFU/g L. 
monocytogenes .  If no colonies are recovered in the 1:10 dilution, report as 
<10 CFU/g L. monocytogenes . 
  b: If more than 200 typical colonies appe ar on each agar type, the food sample 
may be retested using a higher dilution (i.e., 1:50 or 1:100) to enable a more 
accurate enumeration. This situation m ay occur during an outbreak or when 
there is mass contamination of a food commodity. 
  c: Always use the agar type with the largest number of colonies recovered to 
calculate the  final CFU/ml or CFU/g. 
  d: In the calculation example above , if there are more than 20 presumptive 
colonies per agar type, 5 typical colonies p er plate (up to 15 in total) should be 
confirmed as a representative populati on of presumptive colonies.  When 
confirmed, a ratio count may be applied to all counted colonies. For example, 
if 75 presumptive colonies are counted and the 15 picked are confirmed as L. 
monocytogenes , then the final count used is 75 L. monocytogenes , for a final 
reporting of 375 CFU/ml; similarly, if only 3 of the 15 are confirmed as L. 
monocytogenes , the final count will be 75 x 3/15 = 15 L. monocytogenes , for a 
final reporting of 75 CFU/ml .  
 
   
 7. References  
 
 7.1. Pagotto, F. Daley, E., and Farb er, J.M. 2002.  Enumeration of Listeria 
monocytogenes in foods (MLFP-74). The Compendium of Analytical Methods , 
Volume 3.  Available at http://www .hc-sc.gc.ca/fn-an/res-rech/analy-
meth/microbio/volume3/mflp74-eng.php.   
   7.2 MLFP-74 Supplement. 2004. The Compendium of Analytical Methods , Volume 3. 
Available at http://www.hc-sc .gc.ca/fn-an/res-rech/analy-
meth/microbio/volume3/mflp74-sup-eng.php. 
  7.3 Poysky, F.T., Paranjpye, R.N., Lashbrook, L.C., Peterson, M.E., Pelroy, G.A., and 
Eklund, M.W. 1993.  Selective and diffe rential medium for isolation of Listeria 
monocytogenes from foods.  Journal of Food Protection  56:326-332. 
 
7.4 Warburton, D.W., Farber, J.M., Armstrong, A., Caldeira, R., Hunt, T., Messier, S., 
Plante, R., Tiwari, N.P., and Vinet, J.1991.  A comparative study of the "FDA" 
and "USDA" methods for the detection of Listeria monocytogenes in foods. 
International Journal of Food Microbiology 13:105-118. 
  7.5 Warburton, D.W., Farber, J.M., Armstrong, A., Caldeira, R., Tiwari, N.P., Babiuk, 
T., LaCasse, P., and Read, S. 1991.  A Ca nadian comparative study of modified 
versions of the "FDA" and "US DA" methods for the detection of  Listeria 
monocytogenes.  Journal of Food Protection 54:669-676. 
  7.6 American Public Health Association (APHA).  2001 .  Compendium of Methods 
for the Microbiological Examination of Foods . Fourth edition. Chapter 35. F.P. 
Downes and K. Ito (editors), American Public Health Association, Washington, D.C. 
   7.7 Pagotto, F., E. Daley, J. Farber and D. Warburton. 2001. Isolation of Listeria 
  monocytogenes from All Foods and Environmental Samples  (MFHPB-30) . The 
Compendium of Analytical Methods,   Volume 2. Available at http://www.hc-
sc.gc.ca/fn-an/res-rech/analy-meth/ microbio/volume2/mfhpb30-01-eng.php. 
  7.8 MFHPB-30 Supplement. 2002. The Compendium of Analytical Methods,   Volume 
2. Available at http://www.hc-s c.gc.ca/fn-an/res-rech/analy-
meth/microbio/volume2/mfhpb30-sup-eng.php.  
 
 
     
 Figure 5:  Generic diagram of enumeration procedure 
Test portion (x g or x mL) 
+ 
Diluent for preparation of 1:5 initial suspension 
 
Blend or stomach for 2 minutes 
Inoculate OXA and a second agar type by 
spreading a total of 1mL on to the surface of 3 
plates of each agar type 
Incubate for 48h; checking plates after 24h 
Selection of colonies w ith typical appearance 
Confirmation of t ypical colonies
Interpretation and reporting of results  
  
Policy on Listeria monocytogenes in Ready-to-Eat Foods  
References  
 
Abelson, P., Potter Forbes, M., Hall, G. (2006).  The annual cost of foodborne illness in 
Australia.  Available at:  
http://www.ozfoodnet.gov.au/in ternet/ozfoodnet/publishing.ns f/Content/137D93E765468F17CA
2572130080B157/$File/cost-foodborne.pdf   (Accessed on August 31, 2010).  
 
ACMSF (Advisory Committee on the Micr obiological Safety of Food) .  (2009).  Report on the 
increased incidence of listeriosis in the UK.  Ad Hoc Group on Vulnerable Groups.  Available at:  
http://www.food.gov.uk/news/newsarc hive/2009/sep/acmsflisteria   (Accessed on August 27, 
2010).   
 
Anonymous .  (1985).  Epidemiologic notes and reports  Listeriosis outbreak associated with 
Mexican-style cheese - California.  CDC-MMWR, 34: 357-359.  Available at:  
http://www.cdc.gov/mmwr/preview/mmwrhtml/00000562.htm 
 
Anonymous.   (1998).  Multistate outbreak of listeri osis - United States, 1998. CDC- MMWR, 
47: 1085-1086.  Available at:  http:// www.cdc.gov/mmwr/preview/mmwrhtml/00056024.htm 
 
Anonymous.   (1999a).  Multistate outbreak of listeriosis- United States, 1998-1999.  CDC-
MMWR, 47: 1117.  
 
Anonymous.  (1999b).  Listeria cases linke d to pâté.  Westchester Coun ty Department of Health.  
Available at:  http://www.westchestergov.com/health/PR991230.htm   (Accessed on August 27, 
2010). 
 
Anonymous.  (2002).  Public Health Dispatch: Outbr eak of listeriosis -- Northeastern United 
States, 2002.  CDC-MMWR, 51:  950-951.  Available at:  
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5142a3.htm    
 
Aureli, P., Fiorucci, G.C., Caro li, D., Marchiaro, G., Novara, O., Leone, L. and Salmaso, S.  
(2000).  An outbreak of febrile gastroenteri tis associated with corn contaminated by Listeria 
monocytogenes.  N. Eng. J. Med., 342: 1236-1241. 
 
Baker, M., Brett, M., Short, P., Calder, L. and Thornton, R.  (1993).  Listeriosis and mussels. CDNZ, 93: 12-15. 
 
Beuchat, L.R. and Brackett, R.E.   (1990).  Inhibitory effects of raw carrots on Listeria 
monocytogenes.  App. Environ. Microbiol., 56: 1734-1742.  
 
Bille, J.  (1990).  Epidemiology of human listeriosis in Europe, with special reference to the 
Swiss outbreak.  In:  Foodborne listeriosis .  Miller, A.J., Smith J.L., and Somkuti G.A. (Eds), 
Society for Industrial Microbiology, Elsevi er Science Publishing Inc., New York. 
  
 Bille, J., Blanc, D.S., Schmid, H., Boubaker, K ., Baumgartner, A., Siegrist, H.H., Tritten, 
M.L., Lienhard, R., Berner, D., Anderau, R., Treboux, M., Ducommun, J.M., Malinverni, 
R. Genné, D, Erard, P.H. and Waespi, U.  (2006).  Outbreak of hu man listeriosis associated 
with Tomme cheese in Northwest Switzerland, 2005.  Euro. Surveill., 11: 91-93.  Available at:  
http://www.eurosurveillance.org/images/ dynamic/EQ/v06n02/v06n02.pdf  (Accessed on August 
27, 2010). 
 
Boggs, J.D., Whitwam, R.E., Hale, L.M., Briscoe, R.P., Kahn, S.E., MacCormack, J.N., 
Maillard, J-M., Grayson, S.C., Sigmon, K.S ., Reardon, J.W., Saah, J.R. and EIS officers, 
CDC.   (2001).  Outbreak of listeriosis associat ed with homemade Mexican-style cheese - North 
Carolina, October 2000 - January 2001.  CD C-MMWR, 50: 560-562.  Available at:  
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5026a3.htm  and in J. Am. Med. Asso., 
286(6): 664-665. 
 
Brett, M.S.Y., Short, P. and McLauchlin, J.   (1998).  A small outbreak of listeriosis associated 
with smoked mussels.  Int. J. Food Microbiol., 43: 223-229. 
 
Büla, C.,  Bille, J. and Glauser, M.P.  (1995).  An epidemic of food- borne listeriosis in western 
Switzerland: Description of 57 cases involvi ng adults.  Clin. Infect. Dis., 20: 66-72. 
 
CFIA (Canadian Food Inspection Agency).  (2009a).   Meat Hygiene Directive: 2009-1.  Chapter 
5.  Control measures for Listeria  in ready-to-eat (RTE) meat  products.  Available at:  
http://www.inspection.gc.ca/english/fssa /meavia/man/direct/2009/direct1e.shtml  (Accessed on 
August 31, 2010).     
 
CFIA (Canadian Food Inspection Agency).  (2009b).  Personal communication.   
 
Carriedo, G.  (2003).  Mexican cheese may cau se listeriosis.  News release from the city of 
Laredo Health Department.  Available at:  http://www.ci.laredo.t x.us/health/News/08-20-
03MexicanCheese/Mexican%20Cheese .htm  (Accessed on August 27, 2010). 
 
Carrique-Mas, J.J., Hökeberg, I., Andersson,  Y., Arneborn, M., Tham, W., Danielsson-
Tham, M.-L., Osterman, B., Leffler, M., Steen, M., Eriksson, E., Hedin, G. and Giesecke, J.   
(2003).  Febrile gastroenteritis after eating on-farm manufactured fresh cheese - an outbreak of 
listeriosis?  Epidemiol. Infect., 130: 79-86. 
 
Chen, Y., Ross, W.H., Scott, V.N. and Gombas, D.E.  (2003).  Listeria monocytogenes .  Low 
levels equal low risk.  J. Food Prot., 66: 570-577. 
 
Clark, C. G., Farber, J., Pagotto, F., Ciampa, N., Doré, K., Nadon, C., Bernard, K., Ng, L.-
K. and the CPHLN.  (2010).  Surveillance for Listeria monocytogenes and listeriosis, 1995-
2004.  Epidemiol. Infect., 138: 559-572.   
 
  
 CAC (Codex Alimentarius Commission).  (2007).  Guidelines on the application of general 
principles of food hygiene to the control of  Listeria monocytogenes in foods.  Annex I: 
Recommendations for an environmental monitoring program for  Listeria monocytogenes in 
processing areas. CAC/GL 61-2007.  Available at:  
http://www.codexalimentarius.ne t/web/more_info.jsp?id_sta=10740   (Accessed on August 31, 
2010).  
 
CAC (Codex Alimentarius Commission).  (2009a).  Proposed Draft Microbiological Criteria for 
Listeria monocytogenes in ready-to-eat foods. - Alinorm 09/32/13 - Appendix II  - Step 5-.  
Available at:  www.codexalimentarius.net/dow nload/report/714/al32_13e.pdf   (Accessed on 
August 31, 2010). 
 
CAC  (Codex Alimentarius Commission). ( 2009b).  Food Hygiene Basic texts, 4th edition.  
Recommended International Code of Practice General Principles  of Food Hygiene. - CAC/RCP 
1-1969, Rev. 4-2003 – Section II – Scope, use and definitions.  
 
Compendium of Analytical Methods.Available at:  http://www.hc-sc.gc.ca/fn-an/res-
rech/analy-meth/microbio/index-eng.php   (Accessed on August 31, 2010). 
 
Cumming, M., Kludt, P., Matyas, B, DeMaria, A., Stiles, T., Han, L., Gilchrist, M., Neves, 
P, Fitzgibbons, E. and Condon, S.  (2008).  Outbreak of Listeria monocytogenes infections 
associated with pasteurized milk from a lo cal dairy - Massachusetts, 2007.  CDC-MMWR, 57: 
1097-1100.  Available at:  http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5740a1.htm   
 
Dalton, C. B., Austin, C., Sobel, J., Hayes, P.S., Bibb, W. F., Graves, L.M., Swaminathan, 
B., Proctor, M.E. and Griffin, P.M.  (1997).  An outbreak of gastro enteritis and fever due to 
Listeria monocytogenes in milk.  N. Engl. J. Med., 336: 100-105. 
 
D'Amico, D.J. and Donnelly, C.W.  (2008).  Enhanced detection of Listeria  spp. in farmstead 
cheese processing environments through dual primary enrichment, PCR, and molecular 
subtyping. J. Food Prot., 71: 2239-2248. 
 
Danielsson-Tham, M.-L., Eriksson, E., Helmersson, S., Leffler, M., Lüdtke, L., Steen, M, 
Sørgjerd, S. and Tham, W.  (2004).  Causes behind a human  cheese-borne outbreak of 
gastrointestinal listeriosis.  Foodborne Pathog. Dis., 1: 153-159. 
 
Dawson, S.J., Evans, M.R.W., Willby, D., Bardwell, J., Chamberlain, N. and Lewis, D.A.  (2006).  Listeria  outbreak associated with sandwich c onsumption from a hospital retail shop, 
United Kingdom.  Eur. Survei ll., 11: 89-91.  Available at: 
http://www.eurosurveillance.org/images/ dynamic/EQ/v06n02/v06n02.pdf (Accessed on August 
27, 2010). 
 
de Valk, H., Vaillant, V., Jacquet, C., Rocourt, J., Le Querrec, F., Stainer, F., Quelquejeu, N., Pierre, O., Pierre, V., Dese nclos, J.-C. and Goulet, V.  (2001).  Two consecutive 
nationwide outbreaks of listeriosis in France, October 1999-February 2000.  Am. J. Epidemiol., 
154: 944-950. 
 
Dorozynski, A.  (2000).  Seven die in French list eria outbreak. Br. Med. J., 320:601.  
 Ericcson, H., Eklow, A., Danielsson-Tham, M. -L., Loncarevic, S., Mentzing, L.-O., Persson 
I., Unnerstad, H. and Tham W.  (1997).  An outbreak of listerio sis suspected to have been 
caused by rainbow trout. J. Clin. Microbiol., 35:  2904-2907.  
 
European Commission Health and Cons umer Protection Directorate-General .  (1999).  
Opinion of the scientific committee on veteri nary measures relating to public health on Listeria 
monocytogenes.  Available at:  http://ec.europa.eu/f ood/fs/sc/scv/out25_en.pdf   (Accessed on 
August 27, 2010). 
 
European Communities.  (2007).  Commission regulations (EC)  No. 1441/2007 of 5 December 
2007 amending Regulation (EC) No 2073/2005 on microbiological criteria for foodstuffs.  
Official Journal of the European Union, L322/12. 
 
Farber, J.M. and Peterkin, P. I.  (1991).  Listeria monocytogenes, a food-borne pathogen.  
Microbiol. Rev.,  55:  476-511.  
 
Farber, J.M. and Peterkin, P. I.  (2000).  Listeria monocytogenes.  Chapter 44.   In: 
Microbiology of Food .  B. Lund, A.  Baird-Parker et al.  (Eds.).  Chapman and Hall.  London, 
UK. pp1178-1232.   
 
Farber, J.M., Daley, E.M., Mackie, M.T. and Limerick, B.  (2000).  A small outbreak of 
listeriosis potentially linked to  the consumption of imitation crab  meat.  Lett. Appl. Microbiol., 
31: 100-104. 
 
Fleming, D.W., Cochi, S.L., MacDonald, K.L., Brondum, J., Hayes, P.S., Plikaytis, B.D., 
Holmes, M.B., Audurier, A., Broome, C.V. and Reingold, A.L.   (1985).  Pasteurized milk as a 
vehicle of infection in an outbreak of listeriosis.  N. Engl. J. Med., 312: 404-407. 
 
FAO/WHO (Food and Agriculture Organization of the United Nations and the World Health 
Organization).  (2004a).  Proposed  draft guidelines on the applica tion of general principles of 
food hygiene to the [control] of Listeria monocytogenes in ready-to-eat foods.  Available at:  
ftp://ftp.fao.org/codex/ccfh37/fh37_05e.pdf  (Accessed on August 31, 2010). 
 
FAO/WHO (Food and Agriculture Organization of the United Nations and the World Health 
Organization).  (2004b).  Risk assessment of Listeria monocytogenes in ready-to-eat foods.  
Available at:  http://www.who.i nt/foodsafety/publica tions/micro/en/mra4.pdf  (Accessed on 
August 31, 2010). 
 
FDA/FSIS  (Center for Food Safety and Applied Nutrition, Food and Drug Administration, U.S. 
Department of Health and Human Services a nd Food Safety and Inspection Service, U.S. 
Department of Agriculture).  (2003).  Quantitative a ssessment of the relative risk to public health 
from foodborne Listeria monocytogenes  among selected categories of ready-to-eat foods.  
Available at:  
http://www.regulations.gov/search/R egs/home.html#documentDetail?R=0900006480828fda  
(Accessed on August 27, 2010). 
 
  
 Fretz, R., Sagel, U., Ruppitsch, W., Pietzka, A. T., Stöger, A., Huhulescu, S., Heuberger, S., 
Pichler, J., Much, P., Pfaff, G., Stark, K, Prager, R., Flieger, A., Feenstra, O. and 
Allerberger, F.   (2010a).  Listeriosis out break caused by acid curd ch eese “Quargel”, Austria 
and Germany 2009.  Euro. Surveill., 15: 19477.  Available at: 
http://www.eurosurveillance.org/ViewArtic le.aspx?ArticleId=19477 (Accessed on August 27, 
2010).  
 
Fretz, R., Pichler, J., Sagel, U., Much, P ., Ruppitsch, W., Pietzka, A.T., Stöger, A., 
Huhulescu, S., Heuberger, S., Appl, G., Werber , D., Stark, K, Prager, R., Flieger, A., 
Karpíšková R., Pfaff, G., and Allerberger, F.  (2010b).  Update:  Mu ltinational listeriosis 
outbreak due to “Quargel”, a sour milk  curd cheese, caused by two different L. monocytogenes  
serotype 1/2a strains, 2009-2010.  Euro. Surveill., 15: 19543.  Available at: http://www.eurosurveillance.org/ViewArtic le.aspx?ArticleId=19543 (Accessed on August 27, 
2010).  
 
Frye, D.M., Zweig, R., Sturgeon, J., Tormey, M ., LeCavalier, M., Lee, I., Lawani, L. and 
Mascola, L.  (2002).  An outbreak of febrile gastroente ritis associated with delicatessen meat 
contaminated with Listeria monocytogenes .  Clin. Infect. Dis., 35: 943-949.  
 
Gaulin, C., Ramsay, D., Ringuette, L. and Ismaïl, J.  (2003).  First docum ented outbreak of 
Listeria monocytogenes  in Quebec, 2002.  Can. Commun. Dis. Rep., 29: 181-186.  Available at:  
http://www.phac-aspc.gc.ca/publicat/ ccdr-rmtc/03vol29/dr2921ea.html   
 
Gillespie, IA., McLauchlin, J., Grant, K.A., Little, C.L., Mithani, V., Penman, C., Lane, C. 
and  Regan, M.  (2006).  Changing pattern of human lis teriosis, England and Wales, 2001-2004.  
Emerg. Infect. Dis., 12: 1361-1366. 
 
Gombas, D.E., Chen, Y., Clavero, R.S. and Scott, V.N.   (2003).  Survey of Listeria 
monocytogenes in ready-to-eat foods.  J. Food Prot., 66:  559-569. 
 
Gottlieb, S.L., Newbern, E.C., Griffin, P.M ., Graves, L.M., Hoekstra, R.M., Baker, N.L., 
Hunter, S.B., Holt, K.,G., Ramsey, F., Head, M., Levine, P., Johnson, G., Schoonmaker-
Bopp, D., Reddy, V., Kornstein, L., Gerwel, M., Nsubuga, J., Edwards, L., Stonecipher, S., 
Hurd, S., Austin, D., Jefferson, M.A., Young, S.D., Hise, K., Chernak, E.D., Sobel, J. and 
the Listeriosis Outbreak Working Group.   (2006).  Multistate outbr eak of listerios is linked to 
turkey deli meat and subsequent changes in US  regulatory policy.  Cli n. Infect. Dis., 42: 29-36. 
 
Goulet, V., Lepoutre, A., Rocourt, J., Cour tieu, A.-L., Dehaumont, P. and Veit, P.  (1993).  
Epidémie de listériose en France - Bilan final et  résultats de l’enquête épidémiologique.  Bull. 
Epidémiol. Heb., 4: 13-14. 
 
Goulet, V.   (1995).  Investigation en cas d'épidémie de listériose.  Méd. Mal. Infect., 25: 184-
190. 
 
Goulet, V., Jacquet, C., Vaillant, V., Rebière, I., Mouret, E., Lorente, C., Maillot, E., 
Staïner, F. and Rocourt, J.  (1995).  Listeriosis from consumpti on of raw-milk cheese.  Lancet, 
345: 1581-1582.  
 Goulet, V., Rocourt, J., Rebiere, I., Jacquet, C ., Moyse, C., Dehaumont, P, Salvat, G. and 
Veit, P.  (1998).  Listeriosis outbreak a ssociated with the consumption of rillettes in France in 
1993.  J. Inf. Dis., 177: 155-160. 
 
Goulet, V., Hedberg, C., Le Monnier, A. and de Valk, H.  (2008).  Increasing incidence of 
listeriosis in France and other European Countries.  Emerg. Infect. Dis., 14: 734-740. 
 
Government of Canada.   (2010a).  Food and Drugs Act.  Available at:  
http://laws.justice.gc.ca/eng/F-27/index.html  (Accessed on August 27, 2010) 
 
Government of Canada.   (2010b).  Food and Drug Regulations.  Available at:  
http://laws.justice.gc.ca/en/showtdm/ cr/C.R.C.-c.870 (Accessed on August 27, 2010). 
 
Health Canada.  (2006).  Guidelines for the safety asse ssment of Novel foods.  Available at:  
http://www.hc-sc.gc.ca/fn-an/le gislation/guide-ld/nf-an/guidelines-ligne sdirectrices-eng.php   
(Accessed on August 31, 2010).  
 
Health Canada.  (2007).  A guide for the preparation of submissions on food additives.  
Available at:  http://www.hc-sc.gc.ca/ fn-an/pubs/guide-eng.php   (Accessed on August 31, 2010). 
 
Health Canada.  (2010a).  It’s Your Health “ Listeria and food safety”.  Available at: 
http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/listeria-eng.php   (Accessed on August 31, 2010).  
 
Health Canada.  (2010b).  It’s Your Health “Food Safety for Pregnant Women” .  Available at:  
http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/food- aliment/pregnant-enceintes-eng.php  (Accessed on 
August 31, 2010).  
 
Health Canada.  (2010c).  It’s Your Health “Food Safe ty for People with Weakened Immune 
Systems”.  Available at:  h ttp://www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/immune-sys-
immunitaire-eng.php  (Accessed on August 31, 2010).  
 
Health Canada.  (2010d).  It’s Your Health “Food Safety for Older Adults”.  Available at:  
http://www.hc-sc.gc.ca/hl-vs/ iyh-vsv/food-aliment/adults-ain es-eng.php  (Accessed on August 
31, 2010).  
 
Health Canada.  (2010e).  MFLP-41.  Environmen tal sampling for the detection of 
microorganisms.   In:  Compendium of An alytical Methods, Vol 3.  Available at:  http://www.hc-
sc.gc.ca/fn-an/res-rech/analy-m eth/microbio/volume3/mflp41-eng.php   (Accessed on September 
13, 2010).  
 
Health Canada .  (2010f).  Listeria monocytogenes  Challenge Testing of Ready-to-Eat 
Refrigerated Foods.  To be published. 
 
Health Canada. (2010g).  To be published. 
                                                                                                                                                                                                                                                                             
Houben, J.H. and Eckenhausen, F.   (2006).  Surface pasteurization of vacuum-sealed 
precooked ready-to-eat meat produc ts.  J. Food Prot., 69: 459-468.  
 Huang, L and Sites, J.  (2008).  Elimination of Listeria monocytogenes on hotdogs by infrared 
surface treatment.  J. Food Sci., 73:M27-M31. 
 
Hurd, S., Phan, Q., Hadler, J., Mackenzie, B., Lance-Parker, S., Blake, P., Deasy, M. 
Rankin, J., Frye, D., Lee, I., Werner, B., Bugia, D., Bidol, S., Stoltman, G., Boulton, M., Widemann, M., Kornstein, L., Reddy, S., Moji ca, B., Guido, F., Huang, A., Vincent, C., 
Bugenhagen, A., Corby, J., Carloni, E., Holcom b, M., Kondracki, S., Woron, R., Zansky, 
S., Smith, P, Dowdle, G.,  Nich ols, C., Smith, F., Gerber, D ., Jones, T., Moore, W., Ahrabi-
Fard, S. and Davis, J.  (2000).  Multistate outbreak of liste riosis --- United States, 2000.  CDC-
MMWR, 49: 1129-1130.  Available at:  http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4950a1.htm   
 
ICMSF (International Commission on Microbiologica l Specifications for Foods).  (1996).  
Listeria monocytogenes.  In:  Microorganisms in Foods 5. Characteristics of Microbial 
Pathogens, Blackie Academic & Professiona l, London (ISBN 0412 47350 X), pages 141-182. 
 
International Food Safety Authorities Network.   (2009).  Listeriosi s outbreak linked to 
chicken wraps.  Personnal communication. 
 
Jacquet, C., Catimel, B., Brosch, R., Buchrieser, C., Dehaumont, P., Goulet, V., Lepoutre, 
A., Veit, P. and Rocourt, J.  (1995).  Investigations related to the epidemic strain involved in 
the French listeriosis outbreak in 199 2.  Appl. Environ. Microbiol., 61: 2242-2246. 
 
Jacquet, C., Saint-Cloment, C, Brouille, F., Catimel, B and Rocourt, J.   (1998).  La listériose 
humaine en France en 1997.  Données du Centre National de Référence des Listeria.  Bull. 
Epidémiol. Hébdomadaire, 33: 142-143. 
 
Jensen, A., Frederiksen, W. and Gerner-Smidt, P.  (1994).  Risk factors for listeriosis in 
Denmark, 1989-1990.  Scand. J. Infect. Dis., 26: 171-178.  
 
Kittson, E.   (1992).  A case cluster of listeriosis in Western Australia with links to pâté 
consumption.  In:  Proceedings of the 11th International symposiu m on the problems of 
listeriosis, Copenhagen, Denmark, pp. 39-40. 
 
Linnan, M.J., Mascola, L., Dong Lou, X., Goulet, V., May, S., Salminen, C., Hird, D.W., 
Yonekura, M.L., Hayes, P., Weaver, R., Auduri er, A., Plikaytis, B.D., Fannin, S.L., Kleks, 
A.  and Broome, C.V.  (1988).  Epidemic listeriosis associat ed with Mexican-style cheese. N. 
Eng. J. Med., 319: 823-828. 
 
Little, C.L., Sagoo, S.K., Gillespie, I.  A., Grant, K. and McLauchlin, J.   (2009).  Prevalence 
and level of Listeria monocytogenes  and other Listeria species in selected retail ready-to-eat 
foods in the United Kingdom.   J. Food Prot., 72: 1869-1877.  
 
Lundén, J., Tolvanen, and Korkeala, H.  (2004).  Human listeriosis outbreaks linked to dairy 
products in Europe.  J. Dair y Sci., 37:(E. Suppl.):E6-E11. 
 
 
 
  
 Lyytikäinen, O., Autio, T, Maijala, R., Ruutu,  P, Honkanen-Buzalski, T, Miettinen, M., 
Hatakka, M., Mikkola, J., Anttila, V-J., Johansson, T., Rantala, L., Aalto, T., Korkeala, H. 
and Siitonen, A.  (2000).  An outbreak of Listeria monocytogenes serotype 3a infections from 
butter in Finland.  J. Infect. Dis., 181: 1838-1841.  
 
MacDonald, P.D.M., Whitwam, R.E., Boggs, J.D., MacCormack, J.N., Anderson, K.L., 
Reardon, J. W., Saah, J.R., Graves, L.M., Hunter, S.B. and Sobel, J.  (2005).  Outbreak of 
listeriosis among Mexican immigran ts as a result of consumption of illicitly produced Mexican-
style cheese.  Clin. In fect. Dis., 40: 677-682. 
 
Makino, S.-I., Kawamoto, K., Takeshi, K., Okada, Y., Yamasaki, M., Yamamoto, S. and 
Igimi, S.  (2005).  An outbreak of food- borne listeriosis due to chees e in Japan, during 2001.  Int. 
J. Food Microbiol., 104: 189-196. 
 
McLauchlin, J.  (1993).  Listeriosis and Listeria monocytogenes.  Environ. Policy and Practice. 
3, 201-214.  
 
McLauchlin, J., Hall, S.M., Velani, S.K., and Gilbert, R.J.  (1991).  Human listeriosis and 
pâté- a possible association. Br. Med. J., 303, 773-775.   
 
McLauchlin, J., Mitchell, R.T., Smerdon, W.J. and Jewell, K.   (2004).  Listeria 
monocytogenes and listeriosis: a review of hazard charac terisation for use in microbiological risk 
assessment of foods.  Int. J. Food Microbiol., 92: 15-33. 
 
Mead, P.S., Dunne, E.F., Graves, L., Wiedmann , M., Patrick, M., Hunter, S., Salehi, E., 
Mostashari, F., Craig, A., Mshar, P., Bannerman, T., Sauders, B.D., Hayes, P., Dewitt, W., Sparling, P., Griffin, P., Morse, D., Slutsker, L. and Swaminathan, B. for the Listeria 
Outbreak Working Group.  (2006).  Nationwide outbreak of lis teriosis due to contaminated 
meat.  Epidemiol. Infect., 134: 744-751. 
 
Meat Industry  (Canadian Meat Council, Canadian Poultr y and Egg Processors Council, Further 
Poultry Processors Association of Canada and the North American Meat Processors) Listeria 
monocytogenes working group.  (2010).  Industry Best Practices for Control of Listeria 
monocytogenes.  To be published.  
 
Miettinen, M.K., Siitonen, A., Heiskanen, P ., Haajanen, H., Bjorkrot h, K.J. and Korkeala, 
H.J.  (1999) .  Molecular epidemiology of an outbreak of febrile gastro enteritis caused by 
Listeria monocytogenes  in cold-smoked rainbow trout.  J. Clin. Microbiol., 37: 2358-2360. 
 
MSSS (Ministère de la santé et des services socia ux du Québec).  (2009).  Listériose.  Available 
at:  http://www.msss.gouv.qc.ca/sujets/santepub/listeriose.php#situation   (Accessed on August 
27, 2010). 
 
Misrachi, A., Watson, A.J. and Coleman, D.   (1991).  Listeria in smoked mussels in Tasmania.  
Comm. Dis. Intell., 15: 427. 
 
Mitchell, D.L.  (1991).  A case cluster of listeriosis in Tasmania. Comm Dis. Intell., 15:427.  
  
 NFI/NFPA (National Fisheries Institute and Na tional Food Processors Associations).  
(2002).  Listeria monocytogenes control manual, Draft 9. Smoked seafood working group.  
Available at: 
http://foodscience.cornell.edu/ cals/foodsci/research/labs/wie dmann/upload/SSWGLMManual.pd
f  (Accessed on August 27, 2010). 
 
Nguyen-the, C. and Lund, B.M .  (1991).  The lethal effect of carrot on Listeria  species.  J. 
Appl. Bacteriol., 70: 479-488. 
 
Olsen, S.J., Patrick, M., Hunter, S.B., Reddy, V., Kornstein, L., MacKenzie, W.R., Lane, 
D., Bidol, S., Stoltman, G.A., Frye, D.M., L ee, I., Hurd, S., Jones, T.F., LaPorte, T.N., 
Dewitt, W., Graves, L., Wiedmann, M., Schoon maker-Bopp, D.J., Huang, A.J., Vincent, C., 
Bugenhagen, A., Corby, J., Carloni, E.R., Holcomb, M.E., Woron, R.F., Zansky, S.M., Dowdle, G., Smith, F., Ahrabi-Fard, S., Ong, A. R., Tucker, N., Hynes, N.A. and Mead, P.  
(2005).  Multistate outbreak of Listeria monocytogenes infection linked to delicatessen turkey 
meat.  Clin. Infect. Dis., 40: 962-967. 
 
Pagotto, F., Ng, L-K., Clark, C., Farber, J. and the Canadian Public Health Laboratory 
Network.  (2006).  Canadian Listeriosis Reference Service.  Foodborne Pathog. Dis., 3: 132-137. 
 
Proctor, M.E., Brosch, R., Mellen, J.W., Garre tt, L.A., Kaspar, C.W. and Luchansky, J.B.   
(1995).  Use of pulsed-field gel el ectrophoresis to link sporadic cases  of invasive listeriosis with 
recalled chocolate milk.  Appl. Environ. Microbiol., 61: 3177-3179. 
 
PHAC (Public Health Agency of Canada).  (2007).  Public Health Agency of Canada Strategic 
Plan 2007-2012, Information - Knowledge - Action.  Available at:  http://www.phac-
aspc.gc.ca/publicat/2007/sp-ps/inde x-eng.php  (Accessed on August 31, 2010). 
 
PHAC (Public Health Agency of Canada).  ( 2009a).  C-EnterNet Annual Report 2007.  
 
PHAC (Public Health Agency of Canada).  (2009b).  Unpublished data. 
 
PHAC (Public Health Agency of Canada).  ( 2009c).  Personal Communication. National 
Notifiable Diseases Database. 
 
PHAC (Public Health Agency of Canada).  (2009d).  Listeria monocytogenes  outbreak.  
Available at:  http://www.phac-aspc.gc.ca/aler t-alerte/listeri a/listeria_2009-eng.php  (Accessed 
on August 31, 2010). 
 
PHAC (Public Health Agency of Canada).  (2010).  Update to 2008 Listeria monocytogenes  case 
numbers.  Available at: http://www.phac-aspc.gc.ca/alert- alerte/listeri a/listeria_20100413-
eng.php  (Accessed on August 31, 2010).  
 
Riedo, F.X., Pinner, R.W., Tosca, M. d., Cartter, M.L., Graves, L.M., Reeves, M.W., Weaver, R.E., Plikaytis, B.D. and Broome, C.V.  (1994).  A point-source foodborne listeriosis 
outbreak:  documented incubation period and possibl e mild illness.  J. Infect. Dis., 170: 693-696. 
 
Roberts, T., Kowalcyk, B, Buck, P., Blaser, M.J., Frenkel, J.K., Lorber, B., Smith, J., Tarr, 
P.I.  (2009).  The long-term health outcomes of selected foodborne pathogens.  Available at:  
 http://www.foodborneillness.org/images/sto ries/cfi_pdfs/CFI_LTHO_PSP_report_Nov2009_FIN
AL.pdf (Accessed on August 31, 2010). 
 
Rocourt, J., Jacquet, C., Brouille, F., Saint-Cloment, C., and Catimel, B.   (1997).  La 
listériose humaine en France en 1995 et 1996.  D onnées du Centre National de Références des 
Listeria.  Bull. Epidémiol. Hébdomadaire, 41: 186-187. 
 
Rooney, J. and Sutherland, P.  (2001).  Independent review of f ood safety in the Hunter area 
health  service.  HAHS Review of  Food Safety.  Personal Communication. 
 
Ryser, E.T. and Marth E. H.   (2007).  Listeria , Listeriosis, and Food Safety.  Third 
edition.CRC Press. 
 
Salamina, G., Donne, E.D., Niccolini, A., Pod a, G., Cesaroni, D., Bucci, M., Fini, R., 
Maldini, M., Schuchat, A., Swaminathan, B., Bibb, W., Rocourt, J., Binkin, N. and 
Salmaso, S.  (1996).  A foodborne outbreak of gastroenteritis involving Listeria monocytogenes.  
Epidemiol. Infect., 117: 429-436. 
 
Salvat, G., Toquin, M.T., Michel, Y., and Colin, P.   (1995).  Control of Listeria 
monocytogenes in the delicatessen industries: the lessons of  a listeriosis outbreak in France.  Int. 
J. Food Microbiol., 25: 75-81. 
 
Schlech, W. F., Lavigne, P.M., Bortolussi, R.A ., Allen, A. C., Haldane, E.V., Wort, A.J., 
Hightower, A.W., Johnson, S.E., King, S.H., Nicholls, E.S. and Broome, C.V.  (1983).  
Epidemic listeriosis - evidence for transm ission by food.  New Eng. J. Med.,  308: 203-206. 
 
Sim, J., Hood, D., Finnie, L., Wilson, M., Graham, C., Brett, M. and Hudson, J.A.   (2002).  
Series of incidents of Listeria monocytogenes non-invasive febrile ga stroenteritis involving 
ready-to-eat meats.  Lett.  Appl. Microbiol., 35: 409-413. 
 
Swaminathan, B. and Gerner-Smidt, P.  ( 2007).  The epidemiology of human listeriosis.  
Microbes and Inf ection, 9: 1236-1243. 
 
Swaminathan, B., Cabanes, D., Zhang, W. and Cossart, P.  (2007).  Listeria monocytogenes .  
Chapter 21.  In:  Food Microbiology: Fundamentals and Frontiers , M.P. Doyle and L.R. 
Beuchat (Eds). ASM Press, Washington, D.C.,  pp 457-491. 
 
Tompkin, R.B., Christiansen, L.N., Shaparis, A.B., Baker, R.L. and Schroeder, J.M.  
(1992).  Control of Listeria monocytogenes in processed meats.  Food Australia, 44: 370-376.  
 
Tompkin, R.B., Scott, V.N., Bernard, D.T., Sveum, W.H. and Gombas, K.S.  (1999).  
Guidelines to prevent post-processing contamination from Listeria monocytogenes . Dairy, Food 
and Environ. Sanit., 19: 551-562. 
 
Tompkin, R.B.  (2002).  Control of Listeria monocytogenes in the food-processing environment.  
J. Food Prot., 64: 709-725. 
 
Watson, C. and Ott, K.  (1990).  Listeria  outbreak in Western Australia. Commun. Dis 
Intelligence, 24: 9-12.  
 Yde, M. and Genicot, A.  (2004).  Use of PFGE to charac terize clonal relationships among 
Belgian clinical isolates of Listeria monocytogenes .  J. Med. Microbiol., 53: 399-402.