Microbiological Data Program - Annual Summary, Calendar Year 2007 

United States 

Department of 

Agriculture 

Agricultural 

Marketing Service 

Science & 

Technology 

Programs 

Microbiological Data Program 

Progress Update and 2007 Data Summary 

Please Visit Our Website at www.ams.usda.gov/mdp
Microbiological Data Program - Annual Summary, Calendar Year 2007 

United States 

Department of 

Agriculture 

Marketing and 

Regulatory 

Programs 

Agricultural 

Marketing 

Service 

1400 Independence Ave. 

Washington, DC 

20250 

AMS-Agricultural Marketing Service 

An Equal Opportunity Provider and Employer 

February 2008 

To the Reader: 

I am pleased to present the USDA Microbiological Data Program 2007 Data 

Summary. In 2007, MDP tested five commodities (alfalfa sprouts, cantaloupe, 

bagged lettuce, green onions, and tomatoes). Bagged lettuce replaced leaf and 

romaine lettuces. 

MDP is a partnership with cooperating State agencies that are responsible for 

sample collection and analyses. In 2007, eleven States participated in the program: 

California, Colorado, Florida, Maryland, Michigan, Minnesota, New York, Ohio, 

Texas, Washington, and Wisconsin. Because together these States represent all 

regions of the country and more than half the Nation’s population, MDP data can 

be used to develop inferences about the national food supply. 

This summary is intended to provide the reader with an overview of data collected 

in 2007 and summarizes program refinements made during that year. MDP data 

are important in developing baseline levels of targeted pathogens in the domestic 

food supply. As a continuous data-gathering program, MDP data can be used to 

identify microbial trends and to develop risk models. 

If you have comments or suggestions on how this summary can be improved, 

please send electronic-mail to amsmpo.data@usda.gov or visit our Web site at 

www.ams.usda.gov/mdp. 

Sincerely, 

Lloyd C. Day 

Administrator 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

Contents

Page No.

Acknowledgements ........................................................................................................................ vii 

Executive Summary ........................................................................................................................ ix

 

Section I. Introduction..................................................................................................................... 1 

 

Section II. Sampling........................................................................................................................ 4 

 

Section III. Laboratory Operations.................................................................................................. 8 

 

Section IV. Database Management ............................................................................................... 11 

 

Section V. Summary of 2007 Data................................................................................................ 11 

References ..................................................................................................................................... 15 

Disclaimer ..................................................................................................................................... 15 

Definitions..................................................................................................................................... 15 

 

iii 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

Figures and Tables

Figures Page No. 

 1 MDP Program Planning and Program Testing Operations........................................... 2 

 2 Program Participants .................................................................................................... 3 

 3 Commodity Origin ........................................................................................................ 6 

 

4 MDP Data Pathway .................................................................................................... 10 

 

Tables

 1 Distribution of Imported Samples ............................................................................... 5 

 

 2 Samples Collected and Analyzed by State .................................................................. 7 

 3 Summary of Sample Analysis for Pathogenic E. coli .............................................. 12 

 4 Characterization of Pathogenic E. coli Isolates Screened by mPCR......................... 13 

 5 Summary of Analysis for Salmonella........................................................................ 14 

 6 Salmonella Identification and Serogroup ................................................................. 14 

v 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

vii 

Data presented in this report were collected and processed through the efforts of the following 

organizations: 

State Agencies

California Department of Pesticide Regulation 

Colorado Department of Agriculture 

Florida Department of Agriculture and Consumer Services 

Maryland Department of Agriculture 

Michigan Department of Agriculture 

Minnesota Department of Agriculture 

New York Department of Agriculture and Markets 

Ohio Department of Agriculture 

Texas Department of Agriculture 

Washington State Department of Agriculture 

Wisconsin Department of Agriculture, Trade and Consumer Protection 

Laboratories

 

Colorado Department of Agriculture 

Inspection & Consumer Services Division 

Laboratory Section 

2331 West 31st Ave. 

Denver, CO 80211-3859 

Florida Department of Agriculture and Consumer Services 

Bureau of Food Laboratories, Bldg. 9 

3125 Conner Blvd. 

Tallahassee, FL 32399-1650 

Michigan Department of Agriculture 

Laboratory Division 

1615 South Harrison Rd. 

East Lansing, MI 48823-5224 

 Minnesota Department of Agriculture 

Laboratory Services Division 

601 Robert Street North 

St. Paul, MN 55155-2531 

New York Department of Agriculture and Markets 

Food Laboratory 

1220 Washington Ave. 

State Office Campus, Bldg. 7 

Albany, NY 12235 

Acknowledgements 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

Ohio Department of Agriculture 

Consumer Analytical Laboratory Bldg. 3 

8995 East Main St. 

Reynoldsburg, OH 43068 

U.S. Department of Agriculture 

Agricultural Marketing Service 

National Science Laboratory 

801 Summit Crossing Pl. 

Gastonia, NC 28054 

Washington State Department of Agriculture 

3939 Cleveland Ave., SE. 

Olympia, WA 98501 

Wisconsin Department of Agriculture, Trade 

 and Consumer Protection 

Bureau of Laboratory Services 

4702 University Ave. 

Madison, WI 53705 

Program Administration

U.S. Department of Agriculture 

Agricultural Marketing Service 

Deputy Administrator, Science and Technology Programs: 

Robert L. Epstein 

1400 Independence Ave., SW., Room 1090-S 

Washington, DC 20250 

Director: 

Martha Lamont 

Monitoring Programs Office 

8609 Sudley Rd., Ste. 206 

Manassas, VA 20110 

(703) 330-2300 x 117, Facsimile (703) 369-0678 

E-mail: amsmpo.data@usda.gov

Web site: www.ams.usda.gov/mdp

viii 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

ix 

In 2001, the U.S. Department of Agriculture 

(USDA) Agricultural Marketing Service 

(AMS) was charged with implementing 

microbiological testing of fresh fruit and 

vegetables in the United States. The 

program’s mission is to provide statistically 

reliable information regarding targeted 

foodborne pathogens and indicator organisms 

on fresh fruit and vegetables. The 

Microbiological Data Program (MDP) is a 

voluntary data-gathering program, not a 

regulatory enforcement effort. 

AMS coordinates MDP planning and program 

requirements on a continual basis with the 

Centers for Disease Control and Prevention 

(CDC), the Food and Drug Administration 

(FDA), and the USDA National Agricultural 

Statistics Service (NASS). The USDA 

Agricultural Research Service (ARS) and 

Food Safety and Inspection Service (FSIS) 

provide consultation as independent research 

authorities on laboratory methods. The 

participating States are an important 

component of MDP program planning 

activities, particularly those involving 

technical and quality assurance (QA) issues. 

MDP collects produce samples from terminal 

markets and wholesale distribution centers on 

a year-round basis. The MDP sampling frame 

is designed to take into account population 

and consumption on a national scale. In 2007, 

11 States collected fruit and vegetable 

samples (California, Colorado, Florida, 

Maryland, Michigan, Minnesota, New York, 

Ohio, Texas, Washington, and Wisconsin). 

The program tested five commodities (alfalfa 

sprouts, cantaloupe, fresh pre-cut bagged 

lettuce, green onions, and tomatoes) for 

generic Escherichia coli (E. coli), nonO157:H7 E. coli carrying shiga toxins and 

enterotoxins, E. coli O157:H7, and 

Salmonella. The laboratories also tested fresh 

Executive Summary 

pre-cut bagged lettuce samples for coliform 

bacteria. 

MDP began sampling operations in April 

2007 due to delays in the release of funds. 

Sampling operations ceased in September 

2007 due to budget uncertainty for FY 2008; 

however, projects essential for efficient 

program and laboratory operations were 

continued using remaining FY 2007 funds. 

Results of the monitoring effort presented in 

this summary cover program operations from 

April through September 30, 2007. Projects 

were conducted during the period of October 1 

through December 31, 2007. 

MDP analyzed a total of 5,279 samples in 5 

months of sampling and analytical operations. 

Sixty-nine percent of the samples were from 

domestic sources, 26 percent were imported, 

and 5 percent were of unspecified origin. MDP 

identified four samples with E. coli carrying 

shiga toxin; however, pathogenic E. coli

strains were isolated from only two samples. 

These isolates were sent to Pennsylvania State 

University for further characterization, 

including serotyping and testing for different 

virulence-specific genes associated with seven 

different categories of pathogenic E. coli. 

FDA’s Center for Veterinary Medicine (CVM) 

facility conducted tests on antimicrobial 

resistance and genomic fingerprinting on these 

isolates. MDP screening for Salmonella spp. 

resulted in 40 positive samples and from these, 

three Salmonella isolates were reported from 

two alfalfa sprouts samples and one 

cantaloupe sample. 

A number of important benefits are expected 

from MDP. Microbiological data obtained 

from this fresh produce screening effort will 

enhance the understanding of the microbial 

ecology of fresh fruit and vegetables in the 

food supply, permit the identification of longterm trends, and contribute significantly to a 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

national produce microbiological baseline. 

MDP baseline data, which in part reflect the 

changes in cultivation, harvesting practices, 

post-harvest handling and packaging of fresh 

produce to meet changing consumer life styles, 

preferences and demands, will help fine-tune 

Good Agricultural Practices. Furthermore, 

baseline data combined with virulence attributes, serotypes, antimicrobial resistance, and 

genomic fingerprints will help collaborators 

such as CDC and FDA in planning public 

health initiatives. 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

1 

I. Introduction 

Fresh produce is recognized as an important 

component of a healthy diet. Because most 

produce is grown in a natural environment, it is 

vulnerable to contamination with pathogens. The 

fact that produce is often consumed raw without 

any type of intervention that would reduce or 

eliminate pathogens prior to consumption contributes to its potential as a source of foodborne 

illness (1, 2). In 2001, Congress authorized

funding for a microbiological monitoring program to establish a microbial baseline for fresh 

produce. 

MDP’s mission is to collect information 

regarding the incidence and identification of 

targeted foodborne pathogens and indicator 

organisms on fresh fruit and vegetables. This 

publication provides an overview of data collected in 2007 and summarizes program 

refinements made during that year. The 

Agricultural Marketing Service (AMS) Monitoring Programs Office (MPO) manages MDP 

and is responsible for administrative, sampling, 

technical, and database activities. 

Figure 1 (a) illustrates MDP program planning 

activities. AMS coordinates its planning and program requirements with the Centers for Disease 

Control and Prevention (CDC) and the Food and 

Drug Administration (FDA). The USDA Agricultural Research Service (ARS) and Food Safety 

and Inspection Service (FSIS) provide consultation as independent research authorities on 

laboratory methods. MDP relies on the expertise 

of scientists from FDA, CDC, and academia. 

AMS and USDA’s National Agricultural 

Statistics Service (NASS) statisticians designed 

sampling plans based on per capita consumption, 

marketplace availability, product origin, and time 

in transit and storage. The participating States are 

an important component of MDP program 

planning activities, including technical and 

quality assurance (QA) issues. 

Figure 1 (b) depicts MDP program testing 

operations. The participating State laboratories and AMS National Science Laboratory 

(NSL) analyze MDP samples collected by 

trained State sample collectors. FDA’s Center 

for Veterinary Medicine (CVM) and 

Pennsylvania State University (PSU) provide 

additional testing services for isolate 

characterization. Information on MDP data 

and isolates is shared with USDA’s ARS and 

FSIS, CDC, and FDA. 

Commodities tested were selected in 

consultation with FDA and were chosen 

because they are high-consumption fruit and 

vegetables in the U.S. diet, are often 

consumed raw, and have been implicated in 

foodborne outbreaks. Commodities tested in 

2007 included: alfalfa sprouts, cantaloupe, 

fresh pre-cut bagged lettuce, green onions, and 

tomatoes. Commodities were tested for 

generic Escherichia coli (E. coli), E. coli

strains with human pathogenic potential 

including E. coli O157:H7, and Salmonella. 

MDP laboratories also performed multiplex 

polymerase chain reaction (mPCR) screening 

for pathogenic E. coli on all samples. Isolates 

of these organisms were sent to specialized 

laboratories for further characterization 

including serotyping, testing for antimicrobial 

resistance and virulence attributes, and 

genomic fingerprinting. Additionally, the 

laboratories screened all fresh pre-cut bagged 

lettuce samples for coliform bacteria. 

Samples were collected in the 11 participating 

States through cooperative agreements with 

their respective agencies (Figure 2). Also 

Microbiological Data Program (MDP) 

Annual Summary, Calendar Year 2007 

This summary consists of the following sections: (I.) Introduction, (II.) Sampling, (III.) Laboratory 

Operations, (IV.) Database Management, (V.) Summary of 2007 Data 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

2 

Food and Drug 

Administration Participating 

States 

(a) MDP Planning 

(b) MDP Program Operations 

Agricultural 

Research 

Service 

Food Safety 

and Inspection 

Service 

National 

Agricultural 

Statistics Service 

Centers for 

Disease Control 

and Prevention 

Agricultural 

Research 

Service 

Participating 

States 

National Science 

Laboratory 

Pennsylvania 

State University 

Food Safety 

and Inspection 

Service 

Centers for 

Disease Control 

and Prevention 

Food and Drug 

Administration / 

Center for Veterinary 

Medicine 

Figure 1. MDP Program Planning and Program Testing Operations. This figure illustrates (a) agencies/

groups that support MDP program policy and planning activities, and (b) agencies/groups that analyze 

MDP samples, isolates, or results. 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

3 

shown in Figure 2 are the 13 neighboring States 

that are in the direct distribution networks for 

the MDP collection States: Alaska, Connecticut, Delaware, Hawaii, Idaho, Massachusetts, 

Nevada, New Jersey, New Mexico, Oklahoma, 

Vermont, Virginia, and Wyoming. Together, 

these States represent over 50 percent of the 

Nation’s population and all geographic regions 

of the country, with significant rural-to-urban 

variability. Therefore, MDP samples are a 

statistically defensible representation of the 

country as a whole. 

Microbiology laboratory services were provided 

by eight States (Colorado, Florida, Michigan, 

Minnesota, New York, Ohio, Washington, and 

Wisconsin) and one USDA AMS facility, NSL. 

Samples collected by California, Maryland, and 

Texas were analyzed by the Ohio and AMS 

NSL laboratories. In addition, the Colorado 

laboratory analyzed cantaloupes and green 

onions collected by Florida. 

USDA is a member of the interagency Task 

Force on Antimicrobial Resistance established 

in 1999 to address antimicrobial resistance, 

which has been identified as a priority food 

safety and public health issue. As such, isolates 

from positive MDP samples were sent to FDA/

CVM for antimicrobial resistance testing. 

These data are being added to the National 

Antimicrobial Resistance Monitoring System 

Figure 2. Program Participants. During 2007, AMS established cooperative agreements with 11 States to 

sample and/or test MDP commodities. Samples collected by California, Maryland, and Texas are analyzed 

by the Ohio laboratory and the National Science Laboratory in Gastonia, North Carolina. In addition, the 

Colorado laboratory analyzed cantaloupes and green onions collected by Florida. States that do not 

participate in MDP’s sampling program but are in the direct distribution networks of the participating 

States are also shown. 

Nevada 

Idaho 

Wyoming 

New 

Mexico 

Hawaii 

Alaska 

Virginia

Delaware 

Connecticut 

Massachusetts 

Michigan 

Vermont 

New Jersey 

New 

York 

Texas 

California 

Oklahoma 

Washington 

Wisconsin 

Florida 

Participating State 

Minnesota 

States where produce is directly marketed from 

Participating States 

Location of Participating State Laboratories (white stars) 

Federal Laboratory (black star) 

Maryland 

Colorado 

Ohio 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

4 

food distribution system. The MDP sampling 

frame is designed to take into account regional 

diversity, population, and consumption on a 

national scale. The sampling rationale was 

developed by MPO in consultation with NASS 

(3), FDA, and CDC. 

Collecting data over time from a range of 

sources permits statistical statements to be 

made about the distribution of targeted 

pathogens within the target population. The 

target population is all units of a commodity 

available at the wholesale level in a 

participating State during a defined timeframe 

(e.g., 1 year). The extension of statistical statements to the distribution of microorganisms 

within the inferential population (the entire 

amount of the commodity actually consumed by 

the U.S. public during the same timeframe) 

requires that strong assumptions be made about 

the relationship between the participating States 

and the U.S. as a whole, and between the 

wholesale and point-of-consumption levels. 

Nevertheless, because the States that participate 

in MDP fully represent the U.S. inferential 

population, and many microorganisms may 

enter the food supply at or before the wholesale 

level, the MDP is a useful and defensible 

baseline survey. 

Alfalfa sprouts, cantaloupes, green onions, and 

tomatoes remained in the program at 2006 

levels. Based on consultations with FDA, fresh 

pre-cut bagged lettuce was introduced in 2007 

replacing leaf and romaine lettuce. The five 

commodities were selected because they are 

high-consumption fruit and vegetables in the 

U.S. diet, are often consumed raw, and have 

been implicated in outbreaks. All samples in a 

State are collected on the same day or within a 

2-day interval. The samples of cantaloupes and 

tomatoes collected from a site consist of three 

individual units of produce generally collected 

from the same container. Fresh pre-cut bagged 

lettuce and alfalfa sprouts samples generally 

represent individual samples. Inferences cannot 

reasonably be made from the sample units to the 

lots from which they originate because the units 

(NARMS) database. Additionally, CVM performs genomic fingerprinting on MDP isolates 

for inclusion in the PulseNet system. 

In 2007, MDP laboratories replaced the 

enzyme-based assay for detection of generic E. 

coli and the Most Probable Number (MPN) 

analysis with an automated system for detection 

and enumeration of E. coli. This new system is 

based on the same unique enzyme assay; 

however, the experimental setup, assay and the 

capture and analysis of data have been 

automated. The automated system allowed the 

laboratories to reduce personnel time by 

streamlining this labor-intensive assay while at 

the same time removing the bias in subjective 

interpretation of results. The automated system 

was also used for screening pre-cut fresh bagged 

lettuce for coliform bacteria; however, the assay 

for detecting coliform bacteria is based on acid 

production due to fermentation and is different 

from the one used for detecting E. coli. 

AMS employed DNA-based screening for 

pathogenic E. coli, including E. coli O157:H7 

and Salmonella. All samples were screened for 

the presence of pathogenic E. coli that harbor 

shiga toxins (STEC) and enterotoxins (ETEC), 

using mPCR technology. STEC and ETEC are 

two groups of E. coli that cause the majority of 

enteric diseases and are therefore important to 

human health. 

As the program evolves, procedures and 

methods are being refined to provide information necessary for making science-based food 

safety decisions. AMS continues to use quicker, 

more reliable, and more sensitive technologies 

for improved microbial detection and improve 

data collection systems for better database 

management. 

II. Sampling 

The goal of the MDP sampling program is to 

obtain a statistical representation of selected 

commodities in the U.S. food supply by 

randomly selecting samples from the national 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

5 

do not provide enough information to generate 

statistically reliable lot estimates. Nevertheless, 

statistical methods can be applied to make 

whole-target-population inferences from the data 

and to compare these inferences over time. 

MDP benefited from the well-established sampling framework of the Pesticide Data Program 

(PDP), a program administered by MPO since 

1991. States that were already providing 

sampling services for PDP also began collecting 

samples for MDP in 2001 and continue, to date, 

through annual cooperative agreements with 

AMS. All sample collectors receive training and 

are provided with factsheets on the commodities 

they collect. The information in each factsheet 

includes acceptable and unacceptable products, 

availability, sample size, and instructions for 

data entry, packaging, and shipping. Additional 

information is provided on specific requirements for packaging samples that are sensitive 

to ethylene. 

The sampling of commodities is conducted at 

distribution centers and terminal (wholesale) 

markets from which food commodities are 

released to supermarkets and grocery stores, 

and include domestic and imported commodities (refer to Table 1 and Figure 3 for sample 

origin information). Samples are collected on a 

year-round basis and typically over at least two 

growing seasons to accommodate differences in 

growing conditions. Sampling is apportioned 

according to population of the participating 

State. That is, the higher the population of the 

State, the greater the number of samples taken. 

The monthly population-based collection numbers are as follows: California, 14; Colorado, 2; 

Florida, 7; Maryland, 4; Michigan, 6; 

Minnesota, 2; New York, 9; Ohio, 6; Texas, 8; 

Washington, 4; and Wisconsin, 2. This 

schedule results in a monthly target of 64 sites 

sampled per commodity. At each site, 3 

samples are collected from the same lot in each 

facility for a total of 192 samples collected 

every month for each commodity. 

Distribution centers and terminal markets in 

each State are selected at random based on 

probability proportional to the site’s distribution volume (i.e., the amount of produce that 

moves through the site). Therefore, the larger 

the site, the greater the chance it will be 

sampled. If the commodity of interest is not 

available at the designated primary site, an 

alternate site may be chosen. MDP does not 

allow samples to be taken from public markets 

or retail stores because of the potential for 

contamination by the consumer and because 

commodity handling practices at this level in 

the distribution chain may vary widely. 

Between April and September 2007, 5,279 

samples were collected from over 260 sites 

across the country and analyzed by MDP 

Commodity Country 

Number of 

Samples 

Cantaloupe Costa Rica 75 

 Guatemala 144 

 Honduras 81 

 Mexico 6 

 TOTAL 306 

 

Green Onions Canada 3 

 Chile 3 

 Guatemala 18 

 Mexico 669 

 TOTAL 693 

 

Lettuce Canada 3 

 Chile 9 

 Mexico/USA 9 

 TOTAL 21 

 

Tomatoes Canada 93 

 Mexico 276 

 TOTAL 369 

Table 1. Distribution of Imported Samples. 

This table details the number of imported 

samples by country of origin and by commodity.
Microbiological Data Program - Annual Summary, Calendar Year 2007 

6 

Figure 3. Commodity Origin. The proportion of domestic, imported or unknown origin for 

each commodity is depicted for samples tested in 2007. 

Domestic 66.7% 

Unknown 4.5% 

Imported 28.8% 

Cantaloupe (1,062 Samples) 

Domestic 30.8% 

Unknown 4.2% 

Imported 65.0% 

Green Onions (1,067 Samples) 

Domestic 91.4% 

Unknown 6.6% 

Imported 2.0% 

Lettuce, Bagged (1,039 Samples) 

Domestic 94.0% 

Unknown 6.0% 

Sprouts (Alfalfa) (1,047 Samples) 

Domestic 61.1% 

Unknown 4.2% 

Imported 34.7% 

Tomatoes (1,064 Samples) 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

collection by overnight delivery so that 

laboratory analysis can begin the following 

day. 

Unlike PDP operations, where specific commodities are sent to laboratories specializing in 

the analysis of a particular commodity, MDP 

laboratory analyses are performed in the same 

State from which the sample was collected. 

Exceptions include California, Maryland, and 

Texas; these State samples are shipped to the 

Ohio laboratory and AMS NSL, Gastonia, 

North Carolina, for analysis. 

Alfalfa sprouts, cantaloupe, fresh pre-cut 

bagged lettuce, green onions, and tomatoes 

were collected and tested as commodities for 

2007. For fresh pre-cut bagged lettuce, all 

lettuce varieties were acceptable, whether 

7 

laboratories. Table 2 provides a detailed 

breakdown of sample numbers collected by 

commodity. 

All samples are selected and bagged using 

aseptic techniques (i.e., sterile latex gloves and 

sterile sample bags). Once bagged, samples 

must be properly identified and tamper-proofed 

to ensure that chain-of-custody requirements are 

met. Sufficient frozen ice packs and the use of 

adequate packing materials for cushioning and 

insulation are required to maintain refrigerated 

temperatures during transport. Sample temperatures and the condition of each sample are 

observed and recorded upon receipt at each 

laboratory. If the integrity of a sample is in 

question, the laboratory will request that the 

particular commodity be sampled again. All 

samples are shipped on the same day as sample 

State 

 

Total E. coli 

E. coli 

O157:H7 Salmonella 

California 237 231 234 237 234 1,173 1,173 1,173 1,173 

Colorado 36 36 36 36 36 180 180 180 180 

Florida 117 120 117 117 120 591 591 591 591 

Maryland 63 66 51 66 63 309 309 309 309 

Michigan 99 102 102 90 98 491 491 491 491 

Minnesota 33 33 33 33 33 165 165 165 165 

New York 150 150 150 150 150 750 750 750 750 

Ohio 96 98 96 96 99 485 485 485 485 

Texas 132 132 120 123 132 639 639 639 639 

Washington 66 66 66 66 66 330 330 330 330 

Wisconsin 33 33 34 33 33 166 166 166 166 

Totals 1,062 1,067 1,039 1,047 1,064 5,279 5,279 5,279 5,279 

Total 

Coliform 

234 

36 

96 

51 

84 

33 

150 

96 

120 

66 

34 

1,000 

Cantaloupe

Green Onions

Lettuce (Bagged)

Tomatoes

Table 2. Samples Collected and Analyzed by State. This table shows the number of samples 

collected by each State by commodity and the total number of collected samples tested for each 

organism. 

Sprouts (Alfalfa)
Microbiological Data Program - Annual Summary, Calendar Year 2007 

8 

single or mixed. Bags containing lettuce 

mixed with spinach or other greens were not 

acceptable. These commodities are harvested 

primarily by hand although some mechanical 

harvesting does occur. Alfalfa sprouts are 

most often grown in drums and packaged in 

controlled environments. The produce may be 

packaged in the field or taken to a 

packinghouse (e.g., tomatoes require classification for color and/or size). At the packinghouse, the produce is cleaned, trimmed, sized, 

sorted, chopped into small pieces for ready-toeat purposes, bagged, wrapped, and chilled for 

preservation until arrival at distribution 

centers and terminal markets. Cleaning is 

typically accomplished with chlorinated water, 

although other disinfecting agents, such as 

ozone, may be used. Some commodities may 

have a food-grade wax applied to replace 

natural waxes removed during washing to help 

prevent water loss. Fungicides may be added 

to the wax or applied separately to retard 

spoilage. Chilling may be accomplished by 

various means such as vacuum cooling, 

hydrovac cooling, room chilling, or forced air 

cooling. After initial chilling, the produce is 

stored under chilled conditions (avoiding 

freezing) and, depending on the commodity, 

under low-oxygen atmospheric conditions 

(primarily carbon dioxide). To minimize 

spoilage and bruising, the produce is often 

harvested before reaching full ripeness. Prior 

to shipment to distribution centers and 

terminal markets, some commodities are often 

artificially ripened using techniques such as 

ethylene oxide gassing. Some shipping 

companies transport produce in refrigerated 

trucks or rail cars; others use ice; still others 

use no method of cooling, depending on the 

commodity. Therefore, MDP data reflect not 

only agricultural practices but also handling 

practices occurring during harvesting, storage 

(including postharvest treatment), bagging, 

and shipping operations. 

 

MDP uses Sample Information Forms (SIFs) 

to document information required for chainof-custody and to capture other information 

needed to characterize the sample. Sample 

collectors use the forms to record information 

such as: (1) State of sample collection, (2) 

collection date, (3) commodity code, (4) testing 

laboratory code, and (5) sample collector name. 

Other information collected includes the country 

of origin of the sample, any production claims 

(such as organic), and any postharvest treatments. 

An electronic SIF (e-SIF) capturing system was 

implemented in 2003 and continues to be used to 

record relevant sample information. A customized software application allows States to capture 

SIFs electronically using laptop or handheld 

computers. Sample information is captured in the 

MDP database files on the same day as sample 

collection. 

 

MDP sampling operations are conducted with the 

use of Standard Operating Procedures (SOPs) designed to provide consistency across the program 

and ensure the integrity of the analytical data. 

SOPs also contain specific instructions for 

sample selection, shipping and handling, and 

chain-of-custody. SOPs are updated as needed 

and serve as a technical reference for conducting 

program sampling reviews to ensure that program 

goals and objectives are met. All program SOPs 

are available on the Internet at www. 

ams.usda.gov/mdp.

III. Laboratory Operations 

Participating microbiology laboratories tested 

samples of MDP commodities for generic E. coli,

E. coli strains carrying shiga toxins and 

enterotoxins, including E. coli O157:H7, and 

Salmonella. MDP laboratories performed mPCR 

screening of all samples for pathogenic E. coli, 

based on the presence of gene coding for shiga 

toxins and enterotoxins. Isolates of these 

organisms were sent to the Gastroenteric Disease 

Center at PSU and FDA/CVM for further 

characterization. Tests performed by PSU and 

FDA/CVM included serotyping, testing for 

antimicrobial resistance and virulence attributes, 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

and genomic fingerprinting. The laboratories 

also participated in the validation of a realtime 

PCR-based screening method for Shigella

detection. 

Upon arrival at the testing facility, samples 

were logged, visually examined for acceptability, and discarded if determined to be damaged 

(decayed, extensively bruised, or spoiled). 

Samples were refrigerated until analysis 

commenced. Laboratories were permitted to 

refrigerate commodities for up to 24 hours to 

allow for different sample arrival times from 

the various collection sites. Only excess soil 

was removed prior to testing. 

All samples were washed in Universal 

Preenrichment Broth (UPB) with 0.1% Tween®

(Polysorbate 80). Cantaloupes, bagged lettuce, 

green onions, and tomatoes were manually 

washed and alfalfa sprouts were blended using 

a Stomacher® blender. For E. coli and coliform 

assays, an AOAC®-certified enzyme-based 

automated TEMPO® system was used for 

detection and enumeration of E. coli and coliform bacteria (bagged lettuce samples only). 

This system uses the standard Most Probable 

Number (MPN) method for enumeration. 

In order to improve pathogen detection, 

cantaloupe, bagged lettuce, and tomato samples 

were soaked overnight. For alfalfa sprouts and 

green onions, any debris/plant material was 

removed from the wash prior to overnight 

incubation. Genomic DNA was extracted from 

each enriched sample and purified for use in 

detecting pathogens via DNA-based PCR 

assays. All samples were screened by mPCR 

procedures for shiga toxin-producing E. coli

(STEC) and entero-toxigenic E. coli (ETEC). 

MDP laboratories used PCR assays and 

automated instruments for the detection of 

Salmonella and enterohemorrhagic E. coli

O157:H7 in produce samples. Cultural 

methods involving selective growth media and 

Immunomagnetic Separation (IMS) technology 

were employed for isolation of target bacteria. 

9 

In addition to cultural methods, automated 

identifications based on biochemical tests and 

serotyping of surface antigens were used in the 

verification of isolates for the target pathogens. 

During 2007, the laboratories assessed 

automated systems for the extraction and 

purification of genomic DNA from bacterial 

cultures in order to streamline the labor-intensive 

preparation of DNA samples for PCR assays. 

MDP also investigated a semi-automated system 

for repetitive sequence-based PCR (rep-PCR) 

DNA fingerprinting. 

The main objectives of the Quality Assurance/

Quality Control (QA/QC) program were to 

ensure the reliability of MDP data and to ensure 

performance equivalency of participating laboratories. Direction for the MDP QA program was 

provided through written SOPs based on FDA’s 

2001 Bacterial Analytical Methods (BAM), 

AOAC® methods, the FSIS Microbiological 

Laboratory Guide, and the Environmental 

Protection Agency’s Good Laboratory Practices. 

MDP analytical methods are published at 

www.ams.usda.gov/mdp. SOPs provide uniform 

administrative, sampling, and laboratory procedures. MDP laboratories participated in the 

proficiency testing of generic E. coli in produce 

samples, administered by MDP. Several MDP 

laboratories also participated in E. coli O157:H7 

and Shigella proficiency testing for foods, 

including produce, administered by the Food 

Emergency Response Network (FERN). 

Positive and negative controls and a sterile 

media blank were required for each sample set. 

MDP laboratories use positive control strains of 

E. coli O157:H7 and Salmonella typhimurium

that carry a gene coding for Green Fluorescent 

Protein (GFP). Expression of the GFP, detected 

by exposing the cultures to ultraviolet light, 

indicates the presence of the control cultures 

without the need for performing lengthy 

biochemical tests. All controls and blanks were 

taken along with the sample cultures from the 

preenrichment step to isolation and identification 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

10 

Figure 4. MDP Data Pathway. An illustration of MDP data path, from sample collection through 

laboratory analysis and reporting. 

- 8 State labs + 1 Federal lab for sample testing 

- Standardized sample preparation 

- Test for specific foodborne pathogens

Laboratory Analysis 

Sample Collection

- Collection in 11 States 

- Samples taken close to consumer 

- Standardized Sample Information Form 

- Data entry on handheld/laptop computers

- Web-based data entry software 

- Import data from other systems 

- Access controlled by user login 

- Extensive data cross-checks 

Laboratory Remote Data Entry (RDE) 

Data Review at HQ 

- Scientists review data on-screen 

- Upload data to central database

Year-end Review 

- Data reconciliation

Internet

Internet 

- Standard & adhoc reporting 

- Annual Summary 

Data Reporting 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

of target isolates using cultural, immunological, 

and serological methods. MDP laboratories 

also used automated instrumentation for 

confirmation of isolates based on biochemical 

reactions. 

A Technical Advisory Group, comprised of 

microbiologists from each participating 

laboratory, provided technical feedback on 

program SOP revisions and addressed technical 

and QA issues. Additionally, MDP consulted 

with scientists from other Federal agencies 

(FDA, ARS and FSIS) and academia on technical issues. For day-to-day QA oversight, each 

participating facility was required to have a 

Quality Assurance Unit (QAU) that operated 

independently from the laboratory staff. 

Preliminary QA/QC review procedures were 

performed onsite by each laboratory’s QAU. 

Final review procedures are performed by MDP 

staff responsible for collating and reviewing 

data for conformance with SOPs. 

Laboratory performance was monitored through 

onsite reviews by MDP staff to determine 

compliance with MDP SOPs. Corrective 

actions, if necessary, were performed as a result 

of onsite reviews. 

IV. Database Management

 

MDP maintains an electronic database that 

serves as a central data repository. The central 

database resides at MPO in Manassas, Virginia. 

The data captured and stored in the MDP 

database include product information and 

analytical findings for each sample collected 

along with QA/QC results for each set of 

samples. The MDP data pathway is depicted in 

Figure 4. 

MDP uses a Web-based Remote Data Entry 

(RDE) system to capture and report MDP data. 

The RDE system is centralized, with all user 

interface software and database files residing in 

Washington, DC. The laboratory users need 

only a Web browser to interface with the RDE 

system. Access to the RDE system is controlled 

11 

through separate user login/password accounts 

and user access rights for the various system 

functions based on position requirements. The 

RDE system utilizes Secure Sockets Layer 

(SSL) technology to encrypt all data passed 

between users’ computers and the central Web 

server. 

A separate Windows®-based system allows 

sample collectors to electronically capture the 

standardized Sample Information Form (SIF) on 

handheld or laptop computers. The e-SIF 

system generates formatted text files containing 

sample information that are e-mailed to MDP 

headquarters and then imported into the Webbased RDE system. 

The RDE data entry screens have extensive 

edits and cross-checks built in to ensure that 

acceptable values are entered for all critical data 

elements. This task is made easier by the 

practice of capturing and storing standardized 

codes for all critical alphanumeric data elements 

rather than their complete names, meanings, or 

descriptions. This coding scheme allows for 

faster and more accurate data entry, saves disk 

storage space, and makes it easy to perform 

queries on the database. The data entry screens 

also perform edits on numeric fields, dates, and 

other character fields to ensure that entries are 

within prescribed boundaries. 

At MDP headquarters, the RDE system allows 

scientists to review and approve the data for 

inclusion in the central database. The central 

MDP database is maintained using Microsoft® 

Access in a Windows® operating environment. 

Access to the central MDP database is limited 

to MDP headquarters personnel and is 

controlled through password protection and user 

access rights. The system is backed up each 

night and back-up tapes are sent to off-site 

storage once a week. 

V. Summary of 2007 Data 

MDP began sampling operations in April 2007 

due to delays in the release of funds. Sampling 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

12 

operations ceased in September 2007 due to 

budget uncertainty for FY 2008. Consequently, 

results presented in this summary cover only 5 

months of program operations. MDP collected 

a total of 5,279 samples--alfalfa sprouts 

(1,047), cantaloupe (1,062), pre-cut fresh 

bagged lettuce (1,039), green onions (1,067), 

and tomatoes (1,064). 

Table 1 specifies the distribution of imported 

samples by commodity and country of origin. 

Figure 3 illustrates the proportion of samples 

that were domestic, imported, and of unknown 

origin for each commodity. Sixty-nine percent 

of the samples were from domestic sources, 26 

percent were imported, and 5 percent were of 

unspecified origin. Table 2 shows the distribution of samples among each commodity and 

collection State. 

All samples were washed or blended (alfalfa 

sprouts) in Universal Preenrichment Broth 

(UPB) in order to streamline the screening 

process for all target bacteria. E. coli and 

coliform (bagged lettuce only) enumerations 

were performed using the automated 

TEMPO® system. A soaking step was implemented for cantaloupe, bagged lettuce, and 

tomatoes to improve pathogen detection. 

Genomic DNA was extracted from each 

enriched sample and purified for use in 

detecting pathogens. The BAX® instrument, an 

automated PCR system, was used for screening

samples for the presence of Salmonella and 

enterohemorrhagic E. coli O157:H7. Similarly, 

an appropriate aliquot of extracted DNA for 

each sample was used in screening for the 

presence of pathogenic E. coli by mPCR (refer 

to Table 3). 

Positive individual samples were cultured for 

isolation and identification of the organism. 

Identification of isolates was confirmed using a 

conventional biochemical testing system, an 

AOAC® performance-tested kit, or a commercial biochemical kit or system, approved by 

MDP. In addition to biochemical identification 

of an isolate, all MDP participating State 

laboratories were required to confirm the 

identification by serotyping. Isolates were then 

sent to FDA/CVM for expanded serotyping, 

antimicrobial resistance testing, and genomic 

fingerprinting. 

Generic E. coli and Pathogenic E. coli

For detection and enumeration of generic E. 

coli, 5,279 samples were screened using the 

automated TEMPO® system and an AOACcertified method. All 5,279 samples were also 

screened for pathogenic E. coli that harbor 

shiga toxins (STEC) and enterotoxins (ETEC) 

Commodity 

Number of 

Samples 

Tested 

Number of Samples 

Screened by mPCR 

Number of 

Pathogenic E. coliPositive Samples 

Cantaloupe 1,062 1,062 1 

Green Onions 1,067 1,067 0 

Lettuce, Bagged 1,039 1,039 2 

Sprouts (Alfalfa) 1,047 1,047 1 

Tomatoes 1,064 1,064 0 

Total 5,279 5,279 4 

Table 3. Summary of Sample Analysis for Pathogenic E. coli. This table 

summarizes the number of samples initially screened for E. coli and further tested 

for pathogenic E. coli and the number of samples that tested positive for pathogenic 

E. coli. 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

13 

(refer to Table 3) using a mPCR assay 

developed by FDA. Four samples were 

identified as positive for pathogenic E. coli

carrying shiga toxin genes. Successful isolation 

of shiga toxin-carrying E. coli strains (STEC) 

was attained from two of these samples. In 

addition to the technological differences 

between the detection by PCR and isolation by 

cultural means, several other factors influence 

the rate of successful isolation, including: an 

overwhelming amount of background microflora in comparison to the small number of 

target bacterial cells, differential growth rates 

of various bacteria, and additional growth 

requirements. 

 

The two isolates were sent to PSU for 

serotyping and further characterization and to 

FDA/CVM for antimicrobial resistance testing. 

PSU conducted tests that included 12 

virulence-specific genes associated with 

different classes of pathogenic E. coli and 

serotyping for somatic O antigens and flagellar 

H antigens. FDA/CVM conducted tests on 

antimicrobial resistance for 15 different 

antibiotics and genomic fingerprinting on these 

isolates. The results of PSU and FDA/CVM 

testing are shown in Table 4. One each of the 

STEC strain was isolated from cantaloupe and 

fresh pre-cut bagged lettuce. Both strains 

carried additional virulence-related genes and 

they were not resistant to any of the 

antimicrobial compounds tested. To characterize 

an isolate as a human pathogen capable of 

causing disease, there must be an interplay of 

several proteins including toxins, encoded by 

respective genes. MDP only identified toxin 

genes; the additional testing required to 

determine the disease-causing potential of these 

isolates is not within the scope of MDP. 

Coliform Bacteria

Coliform bacteria are normally found in large 

numbers in fresh produce samples because 

produce is grown in an open, natural 

environment. However, fresh pre-cut bagged 

lettuce is a ready-to-eat product that is washed 

before packaging. Therefore, only bagged 

lettuce samples were tested for the presence of 

coliform bacteria using the automated TEMPO®

system. In this assay, bacteria that produce acid 

from lactose fermentation are enumerated. The 

data show a significant reduction of coliform 

bacteria when compared to fresh lettuce, 

demonstrating that washing and other steps 

taken in the preparation of ready-to-eat fresh 

pre-cut bagged lettuce greatly reduced the 

number of coliform bacteria normally expected 

in lettuce. 

Serotyping 

Table 4. Characterization of Pathogenic E. coli Isolates Screened by mPCR. This table provides data 

obtained from additional testing of pathogenic E. coli isolates initially screened by MDP laboratories. 

Information includes: pathogenic class, identified toxin genes, and serotyping results. 

Stx-1 and Stx-2 - shiga toxins 1 and 2, respectively 

HlyA - hemolysin A 

Cnf-2 - cytotoxic necrotizing factor 2 

EAggEC - Enteroaggregative E. coli

Neg - no serological reaction; did not react with standard antisera 

Commodity 

Pathogenic 

Class 

Toxic Genes 

Identified O Antigen H Antigen Pulsed-Field Gel Electrophoresis 

Cantaloupe STEC Stx-1, Cnf-2 88 38 

Lettuce, 

Bagged STEC Stx-2, HlyA, EAggEC Neg 8 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

14 

Salmonella

As depicted in Table 5, a total of 5,279 samples 

were screened for Salmonella by BAX-PCR. Of 

these samples, 40 were positive and 3 Salmonella isolates were obtained: 1 from cantaloupe 

and 2 from alfalfa sprouts. These 3 isolates were 

sent to FDA/CVM for identification by 

serotyping, antimicrobial resistance for 15 

antibiotics, and genomic fingerprinting. Table 6 

identifies each isolate and the associated 

serogroup. The isolate from cantaloupe, S. 

tucson, belonging to serogroup H, was resistant 

to sulfisoxazole, an antimicrobial agent. The 

isolates found in alfalfa sprouts, S. dessau, 

belonging to serogroup E4, and S. mbandaka, 

belonging to serogroup C1, were also resistant 

to sulfisoxazole. 

E. coli 0157:H7

No enterohemorrhagic E. coli O157:H7 strain 

was isolated from the 5,279 samples screened, 

although 3 samples tested positive by BAXPCR. In this case, as with pathogenic E. coli

analysis, several factors contribute to successful 

isolation, including the level of background 

microflora versus the number of target bacterial 

cells, differential bacterial growth rates, and 

additional growth requirements. 

Commodity 

Number of Samples 

Tested 

Number of Positive 

Individual Samples 

Number of Positive 

Isolates 

Cantaloupe 1,062 6 1 

Green Onions 1,067 9 0 

Lettuce, Bagged 1,039 6 0 

Sprouts (Alfalfa) 1,047 9 2 

Tomatoes 1,064 10 0 

TOTALS 5,279 40 3 

Table 5. Summary of Analysis for Salmonella. This table shows the number of 

samples screened for Salmonella, the number of positive individual samples, and the 

number of isolates obtained. 

Commodity Genus Species Serogroup Pulsed-Field Gel Electrophoresis 

Cantaloupe Salmonella tucson H 

Sprouts (Alfalfa) Salmonella mbandaka C1 

Sprouts (Alfalfa) Salmonella dessau E4 

Serotype/Identification 

Table 6. Salmonella Identification and Serogroup. This table summarizes the genus, species, and 

serogroup for each of the three Salmonella isolates obtained in 2007. 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

References: 

1. Produce Safety from Production to Consumption: 2004 Action Plan to Minimize Foodborne 

 Illness Associated with Fresh Produce Consumption (October 2004). U.S. Food and Drug 

 Administration, Center for Food Safety and Applied Nutrition, Office of Plant and Dairy 

 Foods, http://www.cfsan.fda.gov/~dms/prodpla2.html

2. E. coli O157:H7 Outbreaks (September 2006, December 2006). U.S. Food and Drug 

 Administration, Center for Food Safety and Applied Nutrition, Office of Plant and Dairy 

 Foods, http://www.cfsan.fda.gov/list.html

3. USDA, Agricultural Marketing Service, Science and Technology Programs, AMS 

 Microbiological Data Program Sampling Rationale and Principles, February 2002 (rev. 2), 

 http://www.ams.usda.gov/science/MPO/SamplingOverview.pdf

4. Bacteriological Analytical Manual (BAM) (2001). U.S. Food and Drug Administration, 

 http://www.cfsan.fda.gov/~ebam/bam-toc.html 

Disclaimer: 

The use of trade, firm, or corporation names, references to published work, and analytical methodology 

referred to in this 2007 Microbiological Data Program Summary is for the information and convenience 

of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department 

of Agriculture of any product, service, or analytical method to the exclusion of others that may be 

suitable. 

Definitions: 

Antimicrobial resistance: The result of microbes changing in ways that reduce or eliminate the 

effectiveness of drugs, chemicals, or other agents to cure or prevent infections. 

AOAC® INTERNATIONAL: An internationally recognized organization that validates and approves 

analytical methods for foods and agriculture. 

Aseptic: Free of microbial contamination. 

Cultural Methods: Use of rich or selective media for the growth and identification of target bacteria. 

Deoxyribonucleic acid (DNA): The molecule that encodes genetic information required to constitute a 

living and reproducing organism. DNA-based technologies exploit the uniqueness in the DNA 

sequences of a given organism in detection and identification methods. 

Enterohemorrhagic E. coli (EHEC): Strains of E. coli that are the primary cause of hemorrhagic colitis 

or bloody diarrhea, which can progress to the potentially fatal hemolytic uremic syndrome. EHEC are 

typified by the production of verotoxin or Shiga toxins (Stx). E. coli O157:H7 is the prototypic EHEC. 

Enterotoxigenic E. coli (ETEC): Strains of E. coli that are the causative agent of travelers’ diarrhea 

and illness characterized by watery diarrhea with little or no fever. Pathogenesis of ETEC is due to the 

production of any of several enterotoxins, including heat-labile enterotoxin and heat-stable toxin. 

15 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

16 

Genomic fingerprinting: Techniques used in the identification and/or classification of organisms 

exploiting the differences in the DNA sequence. 

Green Fluorescent Protein (GFP): Expression of the gene from jelly fish in bacterial control cultures is 

used as a marker. 

Indicator organism: A microorganism or group of microorganisms whose presence indicates 

unsanitary condition or fecal contamination. 

Isolate: Target bacterial strain isolated as a pure culture and identified. 

National Antimicrobial Resistance Monitoring System (NARMS): A collaborative effort among the 

Centers for Disease Control and Prevention, the Food and Drug Administration, and the U.S. 

Department of Agriculture to monitor antimicrobial resistance of human enteric bacteria, including 

Campylobacter, Salmonella, Escherichia coli O157:H7, and Shigella. 

Pathogen: Specific causative agent (e.g., a bacterium or virus) of disease. 

Polymerase Chain Reaction (PCR): A technique used to amplify a specific region of DNA into a large 

number of copies in order to produce enough DNA to be adequately tested. PCR can be used to 

identify, with a very high probability, disease-causing viruses and/or bacteria. Multiplex PCR (mPCR)

involves simultaneous amplification of more than one specific region of DNA or specific genes for 

various analytes. 

Proficiency test sample: Any matrix sample prepared for the purpose of determining biases, accuracy, 

and/or precision among analysts and/or laboratories or of a single analyst or laboratory. 

PulseNet: A national network of local, State, and Federal public health and food laboratories 

coordinated by the Centers for Disease Control and Prevention (CDC) to detect foodborne disease case 

clusters and outbreaks and facilitate identification of the source by standardized genomic fingerprinting 

(molecular subtyping) of various pathogenic bacteria using pulsed-field gel electrophoresis (PFGE) 

technology. 

Serotyping: An antigen and antibody reaction technique that is used to differentiate strains of 

microorganisms based on differences in the antigenic composition of a certain structure such as the cell 

wall components or flagella. 

Shiga toxin: A family of toxins produced by Shigella dysenteriae type I and shiga toxin-producing E. 

coli. These toxins have a cytotoxic effect on intestinal epithelial cells that causes characteristic bloody 

diarrhea. 

Virulence attributes/factors: A bacterial product, usually a protein or carbohydrate (polysaccharide) 

that contributes to virulence or pathogenicity. 

Virulence: The degree or intensity of pathogenicity of an organism as indicated by case fatality rates 

and/or ability to invade host tissues and cause disease. 
Microbiological Data Program - Annual Summary, Calendar Year 2007 

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, 

color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion,

sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived 

from any public assistance program (Not all prohibited bases apply to all programs.) Persons with disabilities who require 

alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s 

TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of 

Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-

6382 (TDD). USDA is an equal opportunity provider and employer. 

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