Patent Publication Number: US-2011052635-A1

Title: Live attenuated salmonella vaccine

Description:
FIELD OF THE INVENTION 
     The present invention relates to attenuated bacterial mutants, in particular attenuated  Salmonella enterica  mutants, and to a live attenuated vaccine comprising same. The double, triple, multiple mutants of the invention advantageously allow a serological distinction between vaccinated animals and (non-vaccinated) animals that have been exposed to a wild-type field such as wild-type field  S. enterica.    
     STATE OF THE ART 
     Salmonellae are Gram-negative, facultative anaerobic, motile, non-lactose fermenting rods belonging to the family Enterobacteriaceae.  Salmonella  are usually transmitted to humans by the consumption of contaminated foods and cause Salmonellosis.  E. coli  is another member of the family Enterobacteriaceae. 
     Salmonellae have been isolated from many animal species including, cows, chickens, turkeys, sheep, pigs, dogs, cats, horses, donkeys, seals, lizards and snakes. 
     95% of the important  Salmonella  pathogens belong to  S. enterica , with  S. enterica  serovar  Typhimurium  ( S. Typhimurium ) and  S. enterica  serovar  Enteritidis  ( S. Enteritidis ) the most common forms. 
       Salmonella  infections are a serious medical and veterinary problem world-wide and cause concern in the food industry. Contaminated food cannot be readily identified. 
     Control of Salmonellosis is important, to avoid potentially lethal human infections and considerable economic losses for the animal husbandry industry. 
     The ubiquitous presence of  Salmonella  in nature complicates the control of the disease just by detection and eradication of infected animals. 
     Several control strategies based on the principles of competitive exclusion and vaccination have been tested to control the infection of e.g. poultry. 
     Vaccination of farm animals is often considered as the most effective way to prevent zoonoses caused by e.g.  Salmonella.    
     Whole-cell killed vaccines and subunit vaccines are used with variable results in the prevention of  Salmonella  infections in animals and in humans. Inactivated vaccines in general provide poor protection against Salmonellosis. 
     Live attenuated  Salmonella  vaccines are potentially superior to inactivated preparations owing to: (i) their ability to induce cell-mediated immunity in addition to antibody responses; (ii) oral delivery with no risk of needle contamination; (iii) effectiveness after single-dose administration; (iv) induction of immune responses at multiple mucosal sites; (v) low production cost; and (vi) their possible use as carriers for the delivery of recombinant antigens to the immune system. 
     The following attenuated mutant strains have been tested on their efficiency to induce a protective immune response in treated animals: (1) strains carrying mutations in the aro genes (Alderton et .al., 1991 , Avian diseases  35:435-442; Schiemann and Montgomery, 1991 , Veterinary Microbiology  27: 295-308), (2) strains carrying deletions in the cya (adenylate cyclase) and/or crp (cyclic AMP receptor) genes (U.S. Pat. No. 5,389,368; U.S. Pat. No. 5,855,879; U.S. Pat. No. 5,855,880; Hassan and Curtiss, 1997 , Avian Diseases  41:783-791; Porter et al. 1993 , Avian Diseases  37:265-273) and (3) strains that carry mutations in the genes of the guaBA operon of  S. typhi  (Wang et al., 2001 , Infection and Immunity  69:4734-4741; WO99/58146 and U.S. Pat. No. 6,190,669). 
     So far only the vaccine strain Megan® Vacl, that carries deletions in the cya and crp genes, has been effective, at least in part. This strain does not provide full protection (http://www.meganhealth.com/meganvac.html). 
     McFarland and Stocker (1987, Microbial pathogenesis 3:129-141) reported on the virulence of guaA and guaB Tn10 insertion mutants of  S. Typhimurium  and  S. dublin  in BALE/c mice. At high dosage (2.5×10 7  CFU), these authors reported a significant lethality of animals, resulting from the multiplication of the auxotrophic strain. 
     Also the ΔguaBA mutant of  S. typhi  proved no suitable candidate for sound and safe protection against typhoid fever. It showed a significant residual virulence in mice (Wang et al., 2001). 
     There is thus still a need for improved live attenuated  Salmonella  vaccine strains, as well as for improved live attenuated vaccine strains of bacteria infecting veterinary species in general. 
     Vaccinated animals often produce antibodies against different antigens of the pathogen. Problem is that vaccinated animals as such can no longer be distinguished from animals that have been in contact with a wild-type field strain such as a  Salmonella  field strain, and are possibly infected therewith. 
     There is thus also a need for improved live attenuated strains like live attenuated  Salmonella  vaccine strains that would make such distinction possible. 
     AIMS OF THE INVENTION 
     An object of the present invention is to provide attenuated  Salmonella enterica  strains with a double or a triple mutation. 
     Another object of the present invention is to provide a live attenuated vaccine against Salmonellosis and methods of treatment based thereon. 
     Yet another object of the present invention is to provide attenuated  Salmonella  strains which are useful as live vector and as DNA-mediated vaccines expressing foreign antigens. Such strains are thus highly suitable for the development of vaccines including polyvalent vaccines. 
     Still another object of this invention is to provide a method to achieve  S. enterica  deletion mutants of the invention. 
     Still a further object of this invention is to provide an attenuated  Salmonella  strain that allows a serological distinction between vaccinated and non-vaccinated yet possibly infected animals. 
     Yet a further object of this invention is to provide the same materials and methods for the preparation of attenuated strains of a bacterium infecting veterinary species in general, more in particular poultry. 
     The general aim is to improve food safety and animal health. 
     SUMMARY OF THE INVENTION 
     Some ΔguaB auxotrophic  Salmonella enterica  mutants with a deletion mutation in the guaB gene showed residual virulence. It was found that further modifications. (preferably deletions) in one or more genes involved in motility reduced the remaining virulence without affecting the immunogenic capacities of the strain. 
     A first aspect of the invention therefore relates to an attenuated mutant strain of a bacterium infecting veterinary species, in particular an attenuated  S. enterica  mutant strain, wherein said mutant strain contains at least one first genetic modification and at least one second genetic modification, said first modification in one or more (at least one) motility genes, and said second modification in one or more (at least one) genes involved in the survival or the proliferation of the bacterium or pathogen (e.g.  S. enterica ) in the host. The term “bacterium infecting veterinary species” in the context of the invention refers in particular to bacteria that are pathogenic to veterinary species, and which can be attenuated by the above genetic modifications. The bacterium infecting veterinary species may be a Gram-negative bacterium. Preferred are Gram-negative bacteria for poultry such as  Salmonella, Pasteurella, Escherichia coli , etc. Most preferred are  Salmonella enterica  and (pathogenic)  E. coli . By “pathogenic to” is meant that the bacterium, if not attenuated, is capable of causing an infectious disease in the veterinary species. 
     The genetic modifications of the invention advantageously lead to a null-function, in other words impair or affect the gene function. The modification in the present context is also referred to as an “impairing modification”. The modification is said to inactivate the gene in question. Advantageously, said inactivation results in attenuation, at least to a degree that the mutant strain is suitable for use in a live attenuated vaccine. 
     The genetic modification may be an insertion, a deletion, and/or a substitution of one or more nucleotides in said genes. Mutant strains according to the invention by such modification are affected in a motility gene function and in a gene function needed for the survival or the proliferation of the pathogen, leading to a null-function (no functional gene product formed) of the affected genes. 
     Deletion mutants are preferred, as an insertion mutant may revert, thereby restoring the pathogenicity of the strain. 
     The first modification is in one or more (1, 2, 3, . . . ) motility genes. Examples of a gene involved in motility are the genes encoding flagellin. The mutant of the invention may have a (impairing) modification in the fliC and/or the fljB or the fljBA genes respectively (fliC; fljB; fljBA; fliC and fljB; fliC and fljBA; . . . ). Advantageously mutants, in which all genes encoding flagellin are deleted, are incapable of swarming out on LB medium containing 0.4% agar and can thereby easily be distinguished from wild-type motile strains. 
     The second genetic modification is in one or more (1, 2, 3, . . . ) genes involved in the survival or the proliferation of the pathogen in its host. Such gene may be a house-keeping gene or a virulence gene. An example of a housekeeping gene that can lead to attenuated strains when the gene function is affected, is the guaB gene encoding the enzyme IMP dehydrogenase. Such mutant is incapable of forming de novo guanine nucleotides. Also possible are impairing modifications in the guaBA operon, advantageously leading to a null-function of the gene(s) encoding for or regulating proper IMP dehydrogenase activity. 
     Advantageously, the attenuated mutant strains of the invention are immunogenic. 
     The present invention in particular aims to provide attenuated  S. Enteritidis  and  S. Typhimurium  strains. 
     Preferably the genetic modifications of the invention are introduced into parent strain  S. Enteritidis  phage type 4 strain 76Sa88 or into parent strain  S. Typhimurium  1491S96. The 76Sa88 strain is a clinical isolate from a turkey, obtained from the Veterinary and Agrochemical Research Centre, Groeselenberg 99, B-1180 Ukkel, Belgium, harboring the temperature sensitive replication plasmid pKD46, encoding the bacteriophage Lambda Red recombinase system. The 1491S96 strain is a clinical isolate from a chicken. 
     One of the attenuated  S. enterica  strains obtained according to the invention is  S. Enteritidis  strain SM73 having the deposit number deposit number LMG P-21642. Another example is the attenuated  S. Typhimurium  strain SM89 having the deposit number LMG P-21643. 
     A preferred mutant of the invention carries or comprises a genetic modification in the guaB gene and a genetic modification in the fliC gene. 
     Another preferred mutant of the invention carries or comprises a genetic modification in a guaB gene and a genetic modification in the fljBA genes. 
     Yet another preferred mutant of the invention carries or comprises a genetic modification in the guaB gene, a genetic modification in the fliC gene, and a genetic modification in the fljBA genes. 
     The attenuated strains of the invention are highly suitable for use in a live attenuated vaccine. The mutant strains of the invention may encode and express a foreign antigen. 
     Another aspect of the invention relates to a vaccine for immunizing a veterinary species against a bacterial infection, comprising: 
     a pharmaceutically effective or an immunizing amount of an attenuated mutant strain according to the invention; and 
     a pharmaceutically acceptable carrier or diluent. The present invention in particular relates to vaccines comprising attenuated mutant strains of  S. enterica  and/or  E. coli.    
     In general about 10 2  cfu to about 10 10  cfu, preferably about 10 5  cfu to about 10 10  cfu is administered (examples of a pharmaceutically effective or an immunizing amount). An immunizing dose varies according to the route of administration. Those skilled in the art may find that the effective dose for a vaccine administered parenterally may be smaller than a similar vaccine which is administered via drinking water, and the like. 
     The attenuated strains of the invention and pharmaceutical compositions or vaccines comprising same are highly suitable for immunizing animals such as veterinary species, livestock, and more specifically poultry. For instance, the attenuated  Salmonella  strains of the invention, and pharmaceutical compositions or vaccines comprising same, are highly suitable for immunizing veterinary species and in particular poultry such as chicken against Salmonellosis and possibly other diseases (e.g. in the case of a multivalent vaccine). The attenuated strains of the invention are particularly suited to protect the animal/veterinary species in question against an attack by the pathogen (the bacterium infecting veterinary species) in question. 
     A further aspect of the invention therefore concerns a method of immunizing animals, preferably veterinary species, more preferably poultry such as chicken against a disease caused by a bacterium infecting veterinary species, said method comprising the step of: administering to the animal or veterinary species in need thereof an immunizing amount of an attenuated mutant strain of the invention and/or of a vaccine comprising same, whereby a protective immune response is then invoked in the animal or veterinary species. The present invention in particular relates to methods of immunizing veterinary species against Salmonellosis or against an infection by a pathogenic  E. coli.    
     Examples of veterinary species to be immunized against Salmonellosis: poultry, small or heavy livestock such as chicken, turkey, ducks, quails, guinea fowl, pigs, sheep, young calves, cattle etc. An immunizing amount is administered to these animals, preferably via the oral, nasal or parenteral route. 
     A further aspect of the invention relates to a mutant strain of the invention for use as a medicament (e.g. for use in a vaccine). Yet another aspect of the invention relates to the use of an attenuated mutant strain of the invention for the preparation of a medicament, such as a vaccine, for the prevention (and/or treatment) of a disease caused by a pathogen (the bacterium infecting veterinary species) such as Salmonellosis. Examples of animals or veterinary species to be treated and recommended doses are given above. 
     Yet another aspect of the invention concerns the use of mutants of the invention, and in particular flagellin mutants, as serological markers to distinguish between vaccinated animals and animals that are naturally infected, id est have been into contact and became infected by a wild-type strain. 
     The invention for instance relates to a method for a serological distinction between vaccinated animals and animals infected by a wild-type strain, wherein the vaccinated animals have been immunized with a mutant strain wherein a flagellin gene is inactivated, said method comprising the steps of: 
     Assaying animals for the presence of antibodies raised against flagellin, 
     Distinguishing infected animals from vaccinated animals based on the presence or absence of said antibodies. 
     The method of the invention advantageously is an in vitro method. Advantageously animals infected by Salmonellae are as such distinguished from animals that have been immunized with an attenuated live vaccine according to the invention. 
     Livestock, such as poultry and in particular chicken are known to generate antibodies against flagellin gene products and in particular the FliC gene product. The antibodies in question will thus be detected in an animal infected by a wild-type strain (that generates such antibodies), yet not in an animal that has been vaccinated with a mutant strain wherein a flagellin gene(s) is/are inactivated. The latter do not generate antibodies against e.g. FliC and/or FljB. 
     The presence of said antibodies is indicative for the presence of wild-type strains and thus infection. The method of the invention thus advantageously allows detection or diagnosis of a  Salmonella  infection in animals vaccinated by .a mutant strain wherein a flagellin gene(s) is/are inactivated. Such mutant strain may be one of the strains of the invention hereinabove described. 
     Inactivation of flagellin genes such as fliC, thus allows the use of serological tests, e.g. based on the detection of the FliC protein, for the diagnosis of the presence of wild-type strains, such as wild-type  S. enterica , in (vaccinated) animals. In the method of the invention animals are preferably assayed for antibodies against FliC. 
     The method of the invention is in particular applicable to poultry, more preferably chickens. 
     DETAILED DESCRIPTION OF THE INVENTION 
     It was surprisingly found that the combination of a flagellin mutation (an impairing modification in a gene coding for flagellin; also referred to as a flagellar mutation) and an auxotrophic mutation can lead to highly immunogenic attenuated  S. enterica  strains. The mutant strains according to the invention carry or comprise a (at least one) modification(s) in a motility gene(s) and a (at least one) modification(s) in a gene(s) involved in the survival or the proliferation of the pathogen in its host. 
     A gene involved in the survival or proliferation may be a house-keeping gene and/or a virulence gene. Examples of such housekeeping genes and virulence genes can be found in (Mastroeni et al., 2000 , The Veterinary Journal  161:132-164, incorporated by reference herein). A preferred example of a house-keeping gene is the guaB gene, yet a modification in an aro, pur, dap, pab, sipC, phoP, phoQ, pagC, cya, and/or crp gene may also be envisaged. 
     The term “gene” as used herein refers to the coding sequence and its regulatory sequences such as promoter and termination signals. 
     Such inactivation may be obtained via a deletion by which the gene function is impaired. A person skilled in the art knows how to obtain such mutants and a simple test can tell whether the gene function is impaired. For instance, the mutant strain which fails to express a functional guaB gene product cannot grow on Minimal A medium, unless this medium is supplemented with (e.g. 0.3 mM) guanine, xanthine, guanosine or xanthosine. 
     Another simple test can tell whether a motility gene function such as a flagellin gene function is impaired. These mutants do not swarm on LB medium containing 0.4% agar. 
     The modifications in the genes in question should result in attenuation of the mutant strains, preferably at least to a degree that they are suitable for use in a live vaccine. 
     The Examples below show that additional mutations in a (at least one; one or more) motility gene(s) (fliC, fljB and/or fljBA) advantageously alleviated the residual pathogenicity of a guaB deletion mutant, and improved the protection of the immunized animals against challenge with a lethal dose of wild-type  S. enterica.    
     The flagellar filament of all members of the genus  Salmonella  is a multimer of a single protein, the flagellin protein (van Asten et al., 1995 , Journal of Bacteriology  177:1610-2613). 
     FliC is the phase 1 filament subunit protein of flagellin (Clacci-Woolwine et al., 1998 , Infection; and Immunity  66:1127-1134). 
       S. Typhimurium  has two flagellin genes (fliC and fljB) that are located at different sites of the chromosome and that show phase variation. The promoter of fljB forms part of a chromosomal fragment that can be inverted by site-specific recombination. Depending on the orientation, either fljB is expressed together with fljA, the latter encoding a repressor of the fliC gene; or fliC is brought to expression.  E. coli , another member of the Enterobacteriaceae, can also possess two flagellin genes that respectively share homology with the fliC and fljB genes of  S. enterica  (Tominaga, 2004 , Genes Genet. Syst.  79:1-8). 
     Inactivation of the fliC gene in  S. Enteritidis  (encoding the major flagellar protein) increased both the safety and effectiveness of a vaccine administered to the inbred mouse line BALB/c. This line is very sensitive to systemic salmonellosis. 
     This proves amongst others that flagellin is not an essential antigen for the induction of a protective immune response against  Salmonella  in BALB/c mice despite many indications therefore in literature. 
       S. Enteritidis  flagellin is immunogenic in chickens and carries the H:g,m antigenic determinants (van Asten et al., 1995; Wyant et al., 1999 , Infection and Immunity  67:1338-1346; Ogushi et al., 2001 , The Journal of Biological Chemistry  276:30521-30526). 
     There is evidence that flagellae from various species of Gram-negative bacteria (e.g. those of  S. Enteritidis  and  S. typhi ) activate monocytes to produce proinflammatory cytokines (e.g. the tumor necrosis factor alpha) and mediate activation of interleukin-1 receptor-associated kinase (IRAK). 
     It is thus thought that Gram-negative flagellin plays an important and previously unrecognized role in the innate immune response to Gram-negative bacteria. FliC may be of particular importance during the course of infections in the gastrointestinal tract (Clacci-Woolwine et al., 1998; Wyant et al., 1999; Moors et al., 2001 , Infection and Immunity  69:4424-4429). 
     There is a lot of ambiguity in literature as to the degree to which flagella contributes to virulence in poultry and/or humans. 
     Van Asten et al. (2000 , FEMS Microbiol Lett.  185:175-9) have shown that inactivation of the flagellin gene of  S. Enteritidis  strongly reduces (50-fold) invasion into Caco-2 cells (human colon carcinoma cell line), while the bacterial adherence was not really affected. Said report is limited to in vitro results. 
     Parker and Guard-Petter (2001 , FEMS Microbiology Letters  204:287-291) on the other hand found that, upon oral challenge of chicks, a fliC::Tn10 mutant was equally virulent to the wild-type. This indicates that the presence of flagellin was not necessary to achieve at least a moderate level of invasion after oral challenge. When applied subcutaneously, flagellar mutants were significantly attenuated in comparison to the wild-type strain. 
     There are thus a lot of indications in the prior art that teach away from constructing e.g.  S. enterica  double (or triple) mutants according to the invention. Inactivation of one or more motility genes helps reduce the remaining virulence of for instance guaB deletion mutants but there are other advantages as well. 
     The inactivation of e.g. the fliC gene advantageously allows the use of serological tests, based on the detection of antibodies directed against the FliC protein, for the diagnosis of the presence of wild-type  S. enterica , e.g.  S. Enteritidis , in the (vaccinated) animals. Immunodetection is possible via ELISA, via RIA techniques and/or any other known immunological test or format. 
     IDEXX Laboratories has a test on the market (FlockChek®  Salmonella Enteritidis  Antibody Test Kit) to reliably detect antibodies against H-antigenic determinants of the FliC flagellin of  S. Enteritidis  (H:g,m flagellar epitopes). 
     The above demonstrates that double and/or triple  S. enterica  mutants of the invention, bearing a (impairing) genetic modification in a gene involved in survival or the proliferation of the pathogen in the host and in a gene(s) involved in motility have advantages over attenuated  S. enterica  strains that are in the art. 
     The mutant strains of the invention are highly suitable for use in a live attenuated vaccine, as a live vector and/or a DNA-mediated vaccine. The term “vaccine” is meant to include prophylactic as well as therapeutic vaccines. Preferably the vaccine is prophylactic. 
     “Live vector” vaccines, also called “carrier vaccines” and “live antigen delivery systems”, comprise an exciting and versatile area of vaccinology (Levine et al, 1990 , Microecol. Ther.  19:23-32). In this approach, a live viral or bacterial vaccine is modified so that it expresses protective foreign antigens of another microorganism, and delivers those antigens to the immune system, thereby stimulating a protective immune response. Live bacterial vectors that are being promulgated include, among others, attenuated  Salmonella.    
     An object of the invention is to provide attenuated mutant strains for use in a live vaccine, possibly a polyvalent dive vaccine. By a “polyvalent vaccine” or “multivalent vaccine” is meant in particular a vaccine comprising antigenic determinants from a number of different disease-causing organisms. 
     One of the objects of the invention is therefore to provide a vaccine against e.g. Salmonellosis comprising: 
     a pharmaceutically effective or an immunizing amount of an attenuated mutant strain of the invention; and 
     a pharmaceutically acceptable carrier or diluent. 
     Another object of the invention is to provide a live vector vaccine comprising: 
     a pharmaceutically effective or an immunizing amount of an attenuated mutant strain of the invention, wherein said mutant encodes and expresses a foreign antigen; and 
     a pharmaceutically acceptable carrier or diluent. 
     The particular foreign antigen employed in the live vector is not critical to the present invention. 
     Still another object of the invention is to provide a DNA-mediated vaccine comprising: 
     a pharmaceutically effective amount or an immunizing amount of an attenuated mutant strain of the invention; wherein said mutant contains a plasmid which encodes and expresses in a eukaryotic cell, a foreign antigen; and 
     a pharmaceutically acceptable carrier or diluent. 
     Details as to the construction and use of DNA-mediated vaccines can be found in U.S. Pat. No. 5,877,159, which is incorporated by reference herein in its entirety. Again, the particular foreign antigen employed in the DNA-mediated vaccine is not critical to the present invention. 
     The decision whether to express the foreign antigen in the pathogen (using a prokaryotic promoter in a live vector vaccine) or in the cells invaded by the pathogen (using an eukaryotic promoter in a DNA-mediated vaccine) may be based upon which vaccine construction for that particular antigen gives the best immune response in animal studies or in clinical trials, and/or, if. the glycosylation of an antigen is essential for its protective immunogenicity, and/or, if the correct tertiary conformation of an antigen is achieved better with one form of expression than the other (U.S. Pat. No. 5,783,196). 
     By a “pharmaceutically effective amount” is meant an amount much greater than normal to overcome (prevent and/or treat) the disease in question, e.g. Salmonellosis. By an “immunizing amount” as used herein is in fact meant an amount that is able to induce a (protective) immune response in the animal that receives the pharmaceutical composition/vaccine. The immune response invoked may be a humoral, mucosal, local and/or a cellular immune response. As known in the art the necessary amounts may depend on age, sex, weight and many other factors. 
     The particular pharmaceutically acceptable carriers or diluents employed. are not critical to the present invention, and are conventional in the art. Examples of diluents include: buffer for buffering against gastric acid in the stomach, such as citrate buffer (pH 7.0) containing sucrose, bicarbonate buffer (pH 7.0) alone, or bicarbonate buffer (pH 7.0) containing ascorbic acid, lactose, and optionally aspartame. Examples of carriers include: proteins, e.g., as found in skimmed milk; sugars; e.g. sucrose; or polyvinylpyrrolidone. 
     Deletion mutants according to the invention were created via standard homologous recombination techniques, whereby the entire gene(s) or at least part of the genes in question in a first step is replaced by a resistance gene and flanking FRT sites. 
     Preferably, in a second step, said resistance gene is removed by recombination between the two FRT sites. One FRT site and the priming sites P1 and P2 remain by the molecular mechanism of the recombination* removing the antibiotics resistance gene according to Datsenko and Wanner (2000) (see for instance  FIG. 4 ). 
     The invention will be described in further details in the following examples and embodiments by reference to the enclosed drawings. Particular embodiments and examples are not in any way intended to limit the scope of the invention as claimed. The rationale of the examples given here for  S. enterica  are equally well applicable to other (Gram-negative) bacteria infecting veterinary species, more in particular other (Gram-negative) bacteria for poultry such as  Pasteurella , (pathogenic)  E. coli , etc. 
    
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         FIG. 1  gives a schematic overview of the biosynthetic pathway of guanosine monophosphate. 
       AICAR: 5′-phosphoribosyl-4-carboxamide-5-aminoimidazole; ATP: adenosine triphosphate; G: guanine; GMP: guanosine monophosphate; GR: guanosine; Hx: hypoxanthine; HxR: hypoxanthine riboside (inosine); IMP: Inosine monophosphate; X: Xanthine, XMP: Xanthosine monophosphate; guaA: GMP synthetase, guaB: IMP dehydrogenase; guaC: GMP reductase. 
         FIG. 2  represents contig 1294 of the  S. Enteritidis  genome (SEQ ID NO: 19). The ATG initiation codon and TGA termination codon of the guaB gene are in bold. N can be A, C, T or G 
         FIG. 3  represents the sequence of the ΔguaB fragment of  S. Enteritidis  cloned in pUC18 (SEQ ID NO: 20). The primers that were used are indicated by horizontal arrows. The fragment generated with primers GuaB6-GuaB7 was cloned in pUC18. The ATG initiation and TGA termination codon of the guaB gene and the CCCGGG SmaI restriction site are indicated in bold. 
         FIG. 4  represents the nucleotide sequence of the  S. Enteritidis  PCR fragment, which includes the guaB deletion, obtained using primer GuaB10 (SEQ ID NO: 21). The PCR fragment was amplified with primers GuaB6-GuaB7, using total genomic DNA of the mutant SM20. The remaining FRT site is indicated in bold italic and the P1 and P2 primers by arrows (Datsenko and Wanner, 2000 , PNAS  97:6640-6645). The ATG initiation and TGA termination codon of the guaB gene are indicated in bold. 
         FIG. 5  represents the guaB gene of  S. Typhimurium  LT2, section 117 of 220 of the complete genome (SEQ ID NO: 22). The ATG initiation codon and TGA termination codon of the guaB gene are in bold. 
         FIG. 6  shows the nucleotide sequence obtained after sequencing the PCR fragment amplified with primers FliC1-FliC2 on total DNA of the mutants SM73 and SM89, using primer FliC1 and FliC2 (SEQ ID NO: 23). The remaining FRT site is indicated in bold italic, the ATG initiation and TAA stop codons in bold, and P1 and P2 are indicated with arrows. 
         FIG. 7  shows the nucleotide sequence obtained after sequencing the PCR fragment amplified with primers FljBA6-FljBA5 on total DNA of the  S. Typhimurium  mutant SM48, using primer FljBA6 (SEQ ID NO: 24). The remaining FRT site is indicated in bold, P1 and P2 are indicated with arrows. 
         FIGS. 8-11  represent the deposit receipts for SM69, SM73, SM86 and SM89 respectively. 
     
    
    
     EXAMPLES 
     Example 1 
     Auxotrophic Mutation that Affects the guaB Gene 
     An auxotrophic insertion mutant of a wild type  S. Enteritidis  was obtained via insertion mutagenesis. Only when supplemented with 0.3 M guanine, xanthine, guanosine or xanthosine could the mutant strain grow on Minimal A medium. 
     These data strongly suggest that the auxotrophic mutation of the strain affects the guaB gene, encoding the enzyme IMP dehydrogenase (EC 1.1.1.205). This enzyme converts inosine-5′-monophosphate (IMP) into xanthosine monophosphate (XMP) as indicated in  FIG. 1 . 
     An insertion mutant can revert, thereby restoring the pathogenicity of the strain. This can limit its applicability in a live attenuated vaccine. In that aspect deletion mutants are preferred. guaB deletion mutants of  S. Enteritidis  and  S. Typhimurium  were therefore created and tested. The guaB genes of both serovars are given in  FIGS. 2 and 5 . 
     Example 2 
     guaB Deletion Mutants 
     Construction of guaB Deletion Mutants 
     A method to generate deletion mutations in the genome of  E. coli  K12 that was previously published (Datsenko and Wanner, 2000 , PNAS  97:6640-6645) was applied for this aim. This method relies on the homologous recombination, mediated by the bacteriophage λ Red recombinase system, of a linear DNA fragment generated by PCR wherein the guaB sequence is substituted by an antibiotic resistance gene. This resistance gene is surrounded by FRT sites and can be excised from the genome by site-specific recombination, mediated by the FLP recombinase. 
     Overlap PCR (Ho et al., 1989 , Gene  77:51-59) was applied for the deletion of an internal segment of 861 bp of the guaB coding sequence. The principle relies on the use of two primer sets, GuaB3-GuaB4 (flanking the 5′ end of the guaB gene) and GuaB5-GuaB2 (flanking the 3′ end of the guaB gene). Both sets contain primers (GuaB4 and GuaB5) that are partially complementary and to which a SmaI restriction site was added. After annealing of the resulting complementary sequences and chain elongation, PCR with the outward primers GuaB6 and GuaB7 generated a fragment with a 6 basepair SmaI site replacing an 861 basepair internal segment of the guaB coding sequence. This ΔguaB fragment was cloned in the vector pUC18 (see  FIG. 3 ). 
     The chloramphenicol resistance gene (cat) with its flanking FRT sequences was amplified using the primers P1 and P2 (Datsenko and Wanner, 2000) and plasmid pKD3 DNA as a template. This PCR fragment was ligated in the SmaI site of the cloned tguaB fragment. The desired fragment was generated using nested primers (GuaB6-GuaB7). The resulting PCR fragment was electroporated into  S. Enteritidis  76Sa88 harbouring the temperature sensitive replication plasmid pKD46, encoding the bacteriophage Lambda Red recombinase system. The chloramphenicol resistant transformants were tested on Minimal A medium and on Minimal A medium supplemented with 0.3 mM guanine. The ΔguaB::catFRT mutants were confirmed by PCR using the following primer combinations: GuaB6-GuaB7, GuaB6-P2, GuaB7-P1 and P1-P2. 
     The  S. Enteritidis  ΔguaB::catFRT mutant (SM12) was electroporated with the temperature sensitive replication plasmid pCP20, encoding the FLP recombinase, to remove the cat gene. The resulting strain  S. Enteritidis  ΔguaB was named SM20. The PCR fragment in which the deletion is located was obtained using total genomic DNA of the mutant SM20 and the primer combination GuaB6-GuaB7. The ΔguaB mutation was confirmed by sequencing, using the primer GuaB10, of this fragment (see  FIG. 4 ). 
     The sequences of all above-mentioned primers are given in Table 1. 
     To avoid the presence of possible additional mutations, caused by the expression of the Red recombinase system, an isogenic strain was constructed. 
     The ΔguaB::catFRT mutation of the mutant SM12 was transduced with bacteriophage P22 HT int −  (Davis, R. W., Botstein D. and Roth, J. R. (1980)  In Advanced Bacterial Genetics, A manual for genetic engineering . Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.) lysate of SM12 to wild type  S. Enteritidis  76Sa88. The cat gene was removed using the plasmid pCP20. The resulting strain  S. Enteritidis  ΔguaB was called SM69 having deposit number LMG P-21641. 
     A ΔguaB mutant of  S. Typhimurium  strain 1491S96 was constructed using the same procedure and the same primers. The resulting strain was named SM19. SM86 (having the deposit number LMG P-21646) is the isogenic strain obtained after transduction of ΔguaB::catFRT to  S. Typhimurium  strain 1491596 using a bacteriophage P22 HT int −  lysate of SM9, and after excision of the cat gene. 
     The ΔguaB mutants SM19, SM20, SM69 and SM86 are sensitive to bacteriophage P22 HT int − . This proves the presence of intact lipopolysaccharides (LPS). 
     Virulence and Protection Tests with the  S. Enteritidis  guaB Deletion Mutant SM20 in Mice. 
     The virulence of the mutant SM20 in mice was tested by oral infection of 6-8 week old female BALE/c mice (Pattery, et al., 1999 , Mol. Microbiol.  33(4):791-805) in two independent experiments. These were performed as described above. The wild type strain  S. Enteritidis  76Sa88 was tested in parallel as a positive control. The  S. Enteritidis  76Sa88 ΔaroA mutant SM50 was included in the experiment as a vaccine control. This mutant carries a precise deletion of the complete aroA coding sequence and was constructed by the method of Datsenko and Wanner (2000). 
     The complete data are given in Tables 2 and 3. These results demonstrate that the ΔguaB mutant SM20 is strongly attenuated in mice but still shows some residual pathogenicity when administered at this high dose. Oral immunization with this mutant induces protective immunity against infection by a high dose of the corresponding pathogenic wild type  S. Enteritidis  strain 76Sa88. The protection is at least equal to the protection conferred by the  S. Enteritidis  ΔaroA mutant SM50. 
     Virulence and Protection Tests with the Isogenic guaB Deletion Mutants SM69 and SM86 in Mice. 
     The virulence of the mutants SM69 and SM86 in mice was tested by oral infection of 6-8 week old female BALB/c mice. These were performed as described above. The wild type strains  S. Enteritidis  76Sa88 and  S. Typhimurium  1491S96 were tested in parallel as positive controls. 
     The complete data are given in Tables 6, 7, and 10-13. These results demonstrate that the ΔguaB mutants SM69 and SM86 are strongly attenuated in mice, yet still show some residual pathogenicity when administered at this high dose. Oral immunization with the mutants induces protective immunity against infection by a high dose of the corresponding pathogenic wild type strain. 
     Example 3 
     Flagellin Mutants of  S. Enteritidis  and  S. Typhimurium    
     It was then tested whether an additional (a further) modification in a motility gene (e.g. a flagellin gene) could further reduce the residual pathogenicity that remained in single mutants like SM20 that carry a deletion mutation in the guaB gene. 
       S. Enteritidis  strains that contain only one gene coding for flagellin, fliC, were used in preliminary experiments. Double mutants were constructed wherein the guaB and fliC genes of  S. Enteritidis  were inactivated. For  S. Typhimurium , double (ΔguaBΔfliC; ΔguaBΔfljBA) and triple (ΔguaBΔfliCΔfljBA) mutants were constructed. 
     Construction of Af/iC Mutants (SM24, SM30) 
     PCR using the FliCP1-FliCP2 primer combination on the template plasmid pKD3 (catFRT) or pKD4 (kanFRT) amplifies the recombinant fragment which contain the antibiotic resistance gene together with the FRT sites and priming sites P1 and P2, and extensions homologous to the initial 50 (1-50) and the terminal (1468-1518) 50 nucleotides of the fliC coding sequence. In this region,  S. Typhimurium  1491S96 and  S. Enteritidis  76Sa88 show respectively 100% and 98% sequence identity with the primers. The primer FliCP1 contains an additional G at position 37 compared to SEQ ID NO 22. Therefore the ΔfliC mutant allele encodes a 16 amino acid peptide, of which the first 12 amino acids correspond to the amino terminus of FliC. An internal segment of 1416 by (51-1467) of the fliC coding sequence (1-1518) will be substituted. 
     The resulting PCR product (1 μg) was electroporated to  S. Typhimurium  1491S96 (pKD46) and  S. Enteritidis  76Sa88 (pKD46), previously induced with 0.2% arabinose, encoding the Lambda recombinase system. 
     Antibiotic resistant candidate substitution mutants were confirmed by PCR, using primers FliC1 and FliC2 and total DNA of the mutant strains and the wild type strain. Restriction analysis was carried out to distinguish between PCR fragments with approximately the same size. For the restriction of the wild type  S. Typhimurium  PCR fragment amplified with FliC1-FliC2, the enzyme EcoRV was used. Two fragments (470 bp and 1021 bp) were obtained. The fragment amplified for the fliC substitution mutant doesn&#39;t contain an EcoRV restriction site. In case of  S. Enteritidis  the enzyme ApoI was used. This enzyme cuts the wild type fliC fragment of  S. Enteritidis  in 2 pieces (345 bp and 1147 bp). The fragment obtained for the fliC substitution mutant doesn&#39;t contain an ApoI restriction site. 
     The motility of the mutants was tested on LB medium (Miller, 1992, A short course in bacterial genetics, a laboratory manual and handbook for  Escherichia coli  and related bacteria. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.) with 0.4% agar. Wild type  S. Typhimurium  and wild type  S. Enteritidis  swarm on this medium. The  S. Typhimurium  fliC substitution mutant swarms out, as the fljB gene is still present in the mutant. The  S. Enteritidis  fliC substitution mutant doesn&#39;t swarm anymore. These results were confirmed by microscopic observation. 
     Electrocompetent cells of the different mutants were prepared and transformed by electroporation with plasmid pCP20 (extracted from  S. Typhimurium χ 3730, R. Curtiss, III, S. M. Kelly, P. A. Gulig, C. R. Gentry-Weeks and J. E. Galán.  Avirulent Salmonella expressing virulence antigens from other pathogens for use as orally - administered vaccines. In: J. Roth, Editor, Virulence Mechanisms, American Society for Microbiology , Washington D.C. (1988), p. 311) to remove the antibiotic resistance gene. The transformants were incubated at 43° C. This will eliminate the temperature sensitive pCP20 plasmid and should eliminate the antibiotic resistance gene. The loss of the antibiotic resistance gene in  S. Typhimurium  and  S. Enteritidis  ΔfliC::catFRT mutants was confirmed. 
     The deletion mutants, originating from the chloramphenicol resistant substitution mutants, were confirmed by PCR using the primer combination FliC1/FliC2. For both  S. Typhimurium  ΔfliC and  S. Enteritidis  ΔfliC a fragment of 185 bp was amplified. 
     The deletion was confirmed by sequencing the amplified fragments using primer FliC3. 
     The obtained mutants were tested on LB medium containing 0.4% agar: wild type  S. Typhimurium  and wild type  S. Enteritidis  swarms out on this medium, also  S. Typhimurium  ΔfliC swarms out (fljB flagellar gene is still present).  S. Enteritidis  ΔfliC as expected doesn&#39;t swarm out. 
     Construction of ΔfljBA Mutants (SM48) 
       S. Typhimurium  contains a second flagellin gene, fljB. This gene is expressed together with fljA, that codes for the repressor of fliC. In the present case, both fljA and fljB were deleted. FljB is 1520 bp long and codes for the protein flagellin. FljA is 539 bp long and codes for the repressor of fliC. The total length of the fragment that was deleted (fljBA): 2127 bp. 
     Primers were designed which show 51 nucleotides homology with sequences of the fljBA gene and homology with sequences of the template plasmid, which flank the antibiotic resistance gene and FRT sites. Primer FljBAP1 shows homology with the sequence starting from the startcodon of fljB till 51 bp downstream (1-51) and primer FljBAP2 shows homology with the sequence starting from the stop codon of fljA till 51 bp upstream (2076-2127). Primers FljBAP1 and FljBAP2 show homology at their 3′ ends with the priming sites P1 and P2 in the template plasmid flanking the resistance gene with the FRT sites. 
     PCR using primers FljBAP1 and FljBAP2 (sequences in table 1) and template DNA pKD3 (catFRT) or pKD4 (kanFRT) amplified fragments of the desired length. 
     1 μg of the PCR product was electroporated to  S. Typhimurium , transformed with pKD46 or pKD20. The selected kanamycine and chloramphenicol resistant transformants were confirmed by PCR. 
     The mutants were tested on LB medium containing 0.4% agar. Wild type  S. Typhimurium, S. Typhimurium  ΔfljBA::kanFRT and  S. Typhimurium  ΔfijBA::catFRT swarm out (fliC is still present). Motility of the three strains was confirmed by microscopic observation. 
     Electrocompetent cells of the different mutants were electroporated with the pCP20 plasmid (originated from  S. Typhimurium  LT2 restriction mutant χ3730) to remove the antibiotic resistance gene. After 2 hours of incubation at 28° C. the culture was plated on LB medium with carbenicilline. After incubation of the transformants. at 43° C. on LB, they were tested on the loss of the plasmid and the antibiotic resistance gene. The deletion mutations were confirmed by means of PCR and sequencing of the fragment. 
     PCR using primer combination FljBA6/FljBA5 (sequence in table 1) amplified a fragment of 2112 bp for the wild type  S. Typhimurium  and a fragment of 185 bp for the  S. Typhimurium  ΔfljBA mutant SM48. 
     The deletion in mutant SM48 was confirmed by sequencing using primer FljBA6 on the PCR fragment obtained using primers FljBA6-FljBA5 ( FIG. 7 ). 
     Construction of the  S. Typhimurium  1491596 ΔfljBAΔfliC Double Mutant (SM23) 
     The strain  S. Typhimurium  ΔfljBA::kanFRT (pKD46) was used to construct the double mutant. Electrocompetent cells were prepared at a temperature of 28° C. (temperature sensitive plasmid pKD46). The electrocompetent cells were electroporated with the recombinant fliC fragment, in which the fliC gene is substituted with the chloramphenicol resistance gene (see earlier examples). To screen and confirm the candidate mutants the procedure used in the construction of the fliC mutant was followed. The desired genotype:  S. Typhimurium  ΔfljBA::kanFRT ΔfliC::catFRT. To eliminate the antibiotic resistance gene the protocol previously described was followed. The deletions in  S. Typhimurium  ΔfljBA ΔfliC(SM23) were confirmed by PCR. 
     The double mutant  S. Typhimurium  ΔfljBA ΔfliC (SM23) was as expected not motile on LB medium with 0.4% agar. The non-motility of the strain was confirmed by microscopic observation. 
     Combination of the Auxotrophic and the Flagellar Mutations 
     P22-transduction (Davis, R. W., Botstein D. and Roth, J. R. (1980)  In Advanced Bacteria/Genetics, A manual for genetic engineering . Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.) was used to combine the mutations. P22-lysates of the substitution mutants were used to construct the combined deletion mutants. The transduction was confirmed by PCR (the same protocol and primers were used as in previous confirmations). For the elimination of the antibiotic resistance genes the previously described protocol using the pCP20 helper plasmid was used. The deletions were confirmed by PCR. Mutants constructed this way are:  S. Typhimurium  ΔfliC AguaB (SM32),  S. Typhimurium  ΔfljBA ΔguaB (SM35),  S. Typhimurium  ΔfliC ΔfljBA ΔguaB (SM27) and  S. Enteritidis  ΔfliC ΔguaB (SM21). 
     Construction of Isogenic Deletion Mutants 
     To exclude the possibility that additional unknown mutations (which can have an effect on the attenuation of the strains) are present in the candidate vaccine strains, dedicated to the use of the method described by Datsenko and Wanner (2000) for the construction of the deletion mutants, isogenic deletion mutants were constructed. The mutations were transduced to a wild type background, by means of P22 phage transduction (Davis, R. W., Botstein D. and Roth, J. R. (1980)  In Advanced Bacterial Genetics, A manual for genetic engineering . Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.). The antibiotic resistant substitution mutants were used as donor strain. For the elimination of the antibiotic resistance genes and confirmation of the deletions, the same protocols were used as in the previous experiments. 
     Constructed mutants:  S. Enteritidis  ΔguaB (SM69, having the deposit number LMG P-21641);  S. Enteritidis  ΔfliC(SM71);  S. Typhimurium  ΔguaB (SM86, having the deposit number LMG P-21646);  S. Typhimurium  ΔfliC (SM91);  S. Typhimurium  ΔfljBA (SM90),  S. Enteritidis  ΔguaB ΔfliC(SM73, having the deposit number LMG P-21642);  S. Typhimurium  ΔguaB ΔfliC(SM104);  S. Typhimurium  ΔguaB ΔfljBA (SM87);  S. Typhimurium  ΔfljBA ΔfliC (SM83);  S. Typhimurium  ΔguaB ΔfljBA ΔfliC (SM89, having the deposit number LMG P-21643). 
     Example 4 
     Virulence and Protection Experiments with  S. Enteritidis  Vaccine Strains 
     Effect of the Inactivation of the fliC Gene on the Virulence of a  S. Enteritidis  Vaccine Strain. 
     To study the effect of the inactivation of the fliC gene on the immunogenicity of a  S. Enteritidis  vaccine strain, two independent virulence and protection tests were carried out in 7 weeks old female BALB/c mice with both mutant SM20 (ΔguaB) and SM 21 (ΔguaB ΔfliC) (Tables 4 and 5). 
     For the virulence assay, the mice were orally infected with a dose of about 10 8  CFU, which corresponds to approximately 10 5  times the LD 50  of the wild type strain (Pattery et al., 1999 , Molecular Microbiology  33:791-805). The mice were observed during 21 days. All mice inoculated with the wild type  S. Enteritidis  strain 76Sa88 died within 9 days after infection, while the non-infected control mice remained healthy during the observation period of 21 days. In the first experiment mice infected with the  S. Enteritidis  ΔguaB mutant SM20 showed typical disease symptoms (reduced activity, untidy coat and curved back) and one out of ten died. In the second experiment no disease symptoms were observed with SM20. The  S. Enteritidis l ΔguaB ΔfliC mutant SM 21 was asymptomatic in both experiments. 
     Efficacy of the Mutants SM20 and SM21 to Confer Protection: Protection Tests 
     The efficacy of the mutants SM20 and SM21 to confer protection was tested three weeks after the initial immunization by oral challenge with about 10 5  LD50 of the wild type  S. Enteritidis  strain 76Sa88 (LD50=10 3  CFU). The mice were observed during 21 days. All non-immunized mice died after challenge. In the second experiment, one out of three mice vaccinated with SM20 died. All other vaccinated mice survived the challenge without observable disease symptoms. These data show that both mutants are attenuated and confer protection against challenge with the corresponding wild type strain. 
     To ascertain that no additional unknown mutations were present, which could contribute to the attenuation of the candidate vaccine strains, the mutations containing the selectable resistance genes were transferred to a wild type background by P22 transduction (Davis, R. W., Botstein D. and Roth, J. R. (1980)  In Advanced Bacterial Genetics, A manual for genetic engineering . Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.). 
     Efficacy of the Inactivation of the fliC Gene on the Virulence of  S. Enteritidis : Virulence and Protection Tests with Isogenic Strains. 
     The virulence and protection tests in BALE/c mice were repeated with the isogenic strains SM69 (ΔguaB), SM71 (ΔfliC) and SM73 (ΔguaB ΔfliC) after. confirmation by PCR and phenotypic characterization as earlier described. In this virulence assay, a ΔfliC mutant was included, to study the effect of the inactivation of the fliC gene on the virulence of  S. Enteritidis . Similar conditions as described above were used for the virulence and challenge experiments. Data obtained for the transductants SM69 and SM73 (Tables 6 and 7) confirmed the observations made in the earlier experiments. 
     Comparison between both guaB deletion mutants indicates that the  S. Enteritidis  ΔguaB ΔfliC double mutant SM73 is more attenuated and confers better protection against challenge with high doses of the wild type strain than the  S. Enteritidis  ΔguaB single mutant SM69. The virulence assay performed with the  S. Enteritidis  ΔfliC mutant SM71 showed that this mutant remained as virulent as the wild type strain under the applied conditions. 
     Immunological Responses and Antibody Production 
     Fifty-four days following the initial immunization in the first experiment, blood samples were collected from the tail artery of the mice. Anti-lipopolysaccharide (LPS) IgG titers were determined by means of enzyme-linked immunosorbent assay (ELISA) using  S. Enteritidis  LPS (Sigma) for coating. Comparison between sera of mice immunized with SM20 and SM21 showed that in both cases anti-LPS serum IgG responses were elicited and that no significant differences in titer were measured. Oral immunization with a second and third dose, 66 and 95 days after the initial immunization did not enhance the anti-LPS IgG levels in serum (data not shown). 
     Example 5 
     Virulence and Protection Experiments with  S. Typhimurium  Transductants 
     Virulence and protection experiments were carried out with the transductants in 7 weeks old female BALB/c mice. The mice were orally inoculated with approximately 10 8  cells. The mice were observed daily for a period of 21 days. After this period, the mice were challenged with 10 8  cells of the wild type pathogenic strain, and the mice were observed over a period of 21 days. 
     Symptoms of disease and the survival rate are noted in Tables 10-13. The single and double flagellar mutants remained highly virulent when orally administered, all mice died. The mice inoculated with the guaB mutant showed mild symptoms of diseases (mice had been fighting, only two remained alive). The combined ΔguaB ΔfljBA, ΔguaB ΔfliC and ΔguaB ΔfliC ΔfljBA mutants were highly attenuated. No symptoms of disease were observed during the 21 days observation period after vaccination. These mutants conferred good protection after challenge with a high dose of the wild type strain. Only a reduced activity of the mice after challenge can be observed. 
     These results also show that the flagellar mutations do not affect the immunogenic capacities of the strains when administered to BALB/c mice. The flagellar mutations can be useful as a serological marker to distinguish between the vaccine strain and the wild type strain. Combination of the auxotrophic mutation with the flagellar mutation(s) gives the best results concerning the reduced virulence of the mutants in mice and the protection against the corresponding wild type strain. 
     The attenuation of the  S. Typhimurium  ΔguaB ΔfliC ΔfljBA triple deletion mutant and the  S. Typhimurium  double deletion mutants, ΔguaB ΔfljBA and ΔguaB ΔfliC, were comparable. 
     Example 6 
     Safety Evaluation of  S. enteritidis  Vaccine Strains 
     Safety Evaluation SM69 in Chicks Inoculated at the Age of One Day by the Intratracheal or Oral Gavage Route 
     The objective of this study was to evaluate the safety of  S. Enteritidis  ΔguaB mutant strain SM69 master seed in one-day-old chickens. Mortality was used as a primary parameter for the determination of safety. 
     Chicks at one day of age were leg-banded and randomly placed in each of the four treatment groups (Group 1: SM69-IT, group 2: SM69-OG, group 3: PBS-IT and Group 4: PBS-OG). After the master seed inoculation, the birds from groups 1 and 2 were placed in one isolator and those of groups 3 and 4 in another isolator. 
     Chickens in groups 1 and 2 were inoculated with the SM69 master seed by the intratracheal (IT) route or oral gavage (OG) route, respectively, with an actual titer of 1.3×10 8  CFU/0.2 ml per bird. Chickens in groups: 3 and 4 were administered with 0.2 ml PBS (phosphate buffered saline) per bird by the intratracheal or oral gavage, respectively. 
     Following the inoculation of SM69 or PBS, chick mortality was observed daily until 38 days post inoculation. Table 8 summarizes the results of mortality for all 4 groups. In group 1, one bird died during the inoculation due to inoculation trauma. Two birds died at 2 days post inoculation (DPI). Three birds died from day 3 to day 13 (at 3, 5 and 13 DPI respectively). A total of 6 birds thus died in group 1. In group 2, two birds died in total. One died due to inoculation trauma and one died at day 5 post inoculation. No birds died in the PBS treated groups either by the intratracheal or oral gavage route. 
     This study indicates that the  S. Enteritidis  ΔguaB mutant strain SM69 is not safe when administered at 1.3×10 8  CFU per bird at one day of age by the intratracheal or oral gavage route. 
     Safety Evaluation of SM69 in Chicks Inoculated at the Age of 2 Weeks by the Intratracheal or Oral Gavage Route 
     Safety of the  S. Enteritidis  ΔguaB mutant strain SM69 was then evaluated in 2 week-old SPF chickens by the intratracheal and oral gavage routes. Mortality was used as a primary criterion and body weight as a secondary criterion for the determination of safety. 
     Birds at 2 weeks of age were leg-banded and randomly placed in each of the four treatment groups: SM69-IT, SM69-OG, Poulvac ST-IT and PBS-IT. Ten birds in group 1 were inoculated with SM69 by the intratracheal route; ten birds in group 2 were inoculated with SM69 by oral gavage; ten birds in group 3 were inoculated with a  Salmonella Typhimurium  AroA −  vaccine (Poulvac® ST) by the intratracheal route; and five birds in group 4 were inoculated with PBS by the intratracheal route. 
     Chickens in groups 1 and 2 were inoculated with SM69 master seed by the intratracheal or oral gavage route, respectively, with the actual titer of 2.3×10 8  CFU/0.2 ml per bird. Chickens in group 3 were administered with Poulvac® ST by the intratracheal route with 2.2×10 8  CFU/0.2 ml per bird. Chickens in group 4 were administered by the intratracheal route with 0.2 ml PBS per bird. 
     After inoculation, the birds from treatment groups 1 and 2 were placed in one isolator and those from groups 3 and 4 in another isolator. 
     Following inoculations, mortality was observed daily until 21 days post-inoculation. Body weight of all birds was also recorded at the end of the study period (21 days). Poulvac® ST and PBS were used as intratracheal procedure controls. 
     During the 21-day observation period, one bird in the SM69 intratracheal treatment group (group 1) died from an infected yolk sac. No mortality was associated with SM69 inoculation, indicating that the SM69 strain is safe at the titer tested, 2.3×10 8  CFU per bird by the intratracheal and oral gavage routes. As expected, no death was observed either in the Poulvac® ST treated birds at the titer of 2.2×10 8  CFU per bird or in the PBS treated birds, indicating that the study was valid (Table 9). 
     Body weight was compared amongst groups in an analysis of variance (ANOVA) model with body weight as the dependent variable and treatment included as an independent variable. Group comparisons were made using Tukey&#39;s test for multiple comparisons. The level of significance was set at p&lt;0.05. The study was considered valid because the control chickens (PBS control group) remained healthy and free of clinical signs of diseases or mortality throughout the study. 
     There were no significant differences in the final body weight in chickens administered with SM69 by the intratracheal or oral gavage inoculation, Poulvac® ST, or PBS (Table 9). Even though no baseline was established of the birds in each group at one day of age, it was unlikely that there was a significant difference in the initial body weight amongst the four groups since the birds were randomly placed into each of the 4 treatment groups. 
     It can be concluded from the present experiment that SM69 is safe when administered at the tested titer of 2.3×10 8  CFU per bird at 2 weeks of age by either the intratracheal or oral gavage route. 
     Safety Evaluation of SM73 in Chicks Inoculated at the Age of One Day by the Intratracheal or Oral Gavage Route 
     Safety of the  S. Enteritidis  deletion mutant strain SM73 (ΔguaB ΔfliC) was evaluated in chickens by the intratracheal and oral gavage routes. Mortality was used as a primary criterion and body weight as a secondary criterion for the determination of safety. 
     All birds were leg-banded and randomly assigned to one of the four groups of birds included in this study (Group 1: SM73-IT, group 2: SM73-OG, group 3: Poulvac ST-IT and Group 4: PBS-IT). Ten birds in group 1 were inoculated with SM73 by the intratracheal route; ten birds in group 2 were inoculated with SM73 by oral gavage; ten birds in group 3 were inoculated with a  S. Typhimurium  AroA −  vaccine (Poulvac® ST) by the intratracheal route; and five birds in group 4 were inoculated with PBS by the intratracheal route. A total of 4 isolators was used (one for each group) in which the chickens were housed for the duration of the study. 
     Chickens were inoculated at one day of age. Chickens in groups 1 and 2 were inoculated with SM73 master seed by the intratracheal or oral gavage route, respectively, with an actual titer of 2.5×10 7  CFU/0.2 ml per bird. Chickens in group 3 were administered with Poulvac® ST by the intratracheal route with 2.1×10 7  CFU/0.2 ml per bird. Chickens in group 4 were administered by the intratracheal route with 0.2 ml PBS per bird. 
     Mortality was observed and body weight recorded as described above for SM69. Poulvac® ST and PBS were once again used as intratracheal procedure controls. 
     During the 21-day observation period, no mortality was recorded for any bird at all. There was further no difference in the final body weight of PBS-IT, Poulvac ST-IT and SM73-OG inoculated birds. The average body weight of the SM73-IT groups was significantly lower in comparison to the SM73-OG group (p=0.0009) but this is most probably due to an experimental error. 
     It can be concluded from the present experiment that SM73 is safe when administered at the tested titer of a 2.5×10 7  CFU per bird at one day of age by the intratracheal or oral gavage route. 
     A deposit has been made according to the Budapest Treaty at the BCCM/LMG Culture Collection, Laboratorium voor Microbiologie, K. L. Ledeganckstraat 35, B-9000 Gent (Belgium) for the following micro-organisms:  Salmonella Enteritidis  SM69 under deposit number LMG P-21641 (deposit date: 9 Aug., 2002);  S. Enteritidis  SM73 under deposit number LMG P-21642 (deposit date: 9 Aug., 2002),  S. Typhimurium  SM86 under deposit number LMG P-21646 (deposit date: 28 Aug., 2002) and  S. Typhimurium  SM89 under deposit number LMG P-21643 (deposit date: 9 Aug., 2002). The deposits have been made in the name of Prof. J.-P. Hernalsteens, previous address: Vrije Universiteit Brussel, Laboratorium Genetische Virologie, Paardenstraat 65, B-1640 Sint-Genesius-Rhode, current address: Vrije Universiteit Brussel, Onderzoeksgroep Genetische Virologie, Pleinlaan 2, B-1050 Brussels, Belgium. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Primer sequences 
               
            
           
           
               
               
               
            
               
                 SEQ 
                   
                   
               
               
                 ID 
                   
                   
               
               
                 NO 
                 Primer 
                 Sequence 
               
               
                   
               
               
                  1 
                 GuaB2 
                 5′ CGTTCAGGCG CAACAGGCCG TTGT 3′ 
               
               
                   
               
               
                  2 
                 GuaB3 
                 5′ GGCTGCGATT GGCGAGGTAG TA 3′ 
               
               
                   
               
               
                  3 
                 GuaB4 
                 5′ GGTGATCCCG GGCGTCAAAC GTCAGGGCTT 
               
               
                   
                   
                 CTTTA 3′ 
               
               
                   
               
               
                  4 
                 GuaB5 
                 5′ TTGACGCCCG GGATCACCAA AGAGTCCCCG 
               
               
                   
                   
                 AACTA 3′ 
               
               
                   
               
               
                  5 
                 GuaB6 
                 5′ GCAACAACTC CTGCTGGTTA 3′ 
               
               
                   
               
               
                  6 
                 GuaB7 
                 5′ AGACCGAGGA TCACTTTATC 3′ 
               
               
                   
               
               
                  7 
                 GuaB10 
                 5′ AGGAAGTTTG AGAGGATAA 3′ 
               
               
                   
               
               
                  8 
                 P1 
                 5′ GTGTAGGCTG GAGCTGCTTC 3′ 
               
               
                   
               
               
                  9 
                 P2 
                 5′ CATATGAATA TCCTCCTTAG 3′ 
               
               
                   
               
               
                 10 
                 F1iCP1 
                 5′ ATGGCACAAG TCATTAATAC AAACAGCCTG 
               
               
                   
                   
                 TCGCTGGTTG ACCCAGAATA ATGTGTAGGC 
               
               
                   
                   
                 TGGAGCTGCT TC 3′ 
               
               
                   
               
               
                 11 
                 FliCP2 
                 5′ CGCATTAACG CAGTAAAGAG AGGACGTTTT 
               
               
                   
                   
                 GCGGAACCTG GTTMGCCTGC GCCACATATG 
               
               
                   
                   
                 AATATCCTCC TTAG 3′ 
               
               
                   
               
               
                 12 
                 F1iC1 
                 5′ ATGGCACAAG TCATTAATAC AAACAG 3′ 
               
               
                   
               
               
                 13 
                 F1iC2 
                 5′ CGCATTAACG CAGTAAAGAG AGGAC 3′ 
               
               
                   
               
               
                 14 
                 F1iC3 
                 5′ TATCGGCAAT CTGGAGGCAA 3′ 
               
               
                   
               
               
                 15 
                 F1jBAP1 
                 5′ ATGGCACAAG TAATCAACAC TAACAGTCTG 
               
               
                   
                   
                 TCGCTGCTGA CCCAGAATAA CTGTGTAGGC 
               
               
                   
                   
                 TGGAGCTGCT TC 3′ 
               
               
                   
               
               
                 16 
                 FljBAP2 
                 5′ TTATTCAGCG TAGTCCGAAG ACGTGATCCT 
               
               
                   
                   
                 GCTCACCCAG TCAAACATAA CCATATGAAT 
               
               
                   
                   
                 ATCCTCCTTA G 3′ 
               
               
                   
               
               
                 17 
                 FljBA5 
                 5′ CAGCGTAGTC CGAAGACGTG ATC 3′ 
               
               
                   
               
               
                 18 
                 FLjBA6 
                 5′ ACACTAACAG TCTGTCGCTG CT 3′ 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Virulence test in BALB/c mice of the  S. Enteritidis  ΔguaB mutant SM20 
               
            
           
           
               
               
               
               
            
               
                 Infection 
                   
                 Day of 
                   
               
            
           
           
               
               
               
               
               
            
               
                 Strain 
                 Dose 
                 Survival 
                 death 
                 State of the mice 
               
               
                   
               
            
           
           
               
            
               
                 First Experiment 
               
            
           
           
               
               
               
               
               
            
               
                 Negative control: milk 
                 / 
                 11/11 
                 / 
                 No disease symptoms 
               
               
                 Positive control:  S. Enteritidis  76Sa88 
                 2.1 × 10 8   
                 0/5 
                 7, 7, 8, 
               
               
                   
                   
                   
                 8, 9 
               
               
                 Vaccine control:  S. Enteritidis  ΔaroA SM50 
                 2.5 × 10 8   
                 10/10 
                 / 
                 No disease symptoms 
               
               
                   S. Enteritidis  ΔguaB SM20 
                 5.1 × 10 8   
                  9/10 
                 13 
                 Disease symptoms between the 
               
               
                   
                   
                   
                   
                 7 th  and the 14 th  day after 
               
               
                   
                   
                   
                   
                 infection 
               
            
           
           
               
            
               
                 Second Experiment 
               
            
           
           
               
               
               
               
               
            
               
                 Negative control: milk 
                 / 
                 4/4 
                 / 
                 No disease symptoms 
               
               
                 Positive control:  S. Enteritidis  76Sa88 
                 1.4 × 10 8   
                 0/3 
                 8, 9, 9 
               
               
                 Vaccine control:  S. Enteritidis  ΔaroA SM50 
                 2.1 × 10 8   
                 3/3 
                 / 
                 No disease symptoms 
               
               
                   S. Enteritidis  ΔguaB SM20 
                 1.9 × 10 8   
                 3/3 
                 / 
                 No disease symptoms 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Challenge of mice vaccinated with the  S. Enteritidis  guaB mutant SM20 
               
            
           
           
               
               
               
               
            
               
                 Vaccination 
                 Challenge 
                   
                 Day of 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Strain 
                 Dose 
                 Strain 
                 Dose 
                 Survival 
                 death 
                 State of the mice 
               
               
                   
               
            
           
           
               
            
               
                 First Experiment 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Negative 
                 / 
                 negative 
                 / 
                 6/6 
                 / 
                 No disease symptoms 
               
               
                 control: milk 
                   
                 control: milk 
               
               
                 Negative 
                 / 
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 0/5 
                 7, 8, 8, 
                 Disease symptoms starting on 
               
               
                 control: milk 
                   
                 76Sa88 
                   
                   
                 8, 9 
                 the 5 th  day after challenge 
               
               
                 Vaccine control: 
                 2.5 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 3/5 
                 9, 13 
                 Disease symptoms between the 
               
               
                 
                   S. Enteritidis 
                 
                   
                 76Sa88 
                   
                   
                   
                 7 th  and the 14 th  day after 
               
               
                 ΔaroA SM50 
                   
                   
                   
                   
                   
                 challenge 
               
               
                 
                   S. Enteritidis 
                 
                 5.1 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 5/5 
                 / 
                 Mice are less active between 
               
               
                 ΔgucB SM20 
                   
                 76Sa88 
                   
                   
                   
                 the 11 th  and the 14 th  day 
               
               
                   
                   
                   
                   
                   
                   
                 after challenge. 
               
            
           
           
               
            
               
                 Second Experiment 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Negative 
                 / 
                 negative 
                 / 
                 2/2 
                 / 
                 No disease symptoms 
               
               
                 control: milk 
                   
                 control: milk 
               
               
                 Negative 
                 / 
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 0/2 
                 9, 18 
               
               
                 control: milk 
                   
                 76Sa88 
               
               
                 Vaccine control: 
                 2.1 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 1/3 
                 9, 21 
                 Disease symptoms between the 
               
               
                 
                   S. Enteritidis 
                 
                   
                 76Sa88 
                   
                   
                   
                 7 th  and the 21 st  day after 
               
               
                 ΔaroA SM50 
                   
                   
                   
                   
                   
                 challenge. 
               
               
                 
                   S. Enteritidis 
                 
                 1.9 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 2/3 
                 10 
                 Disease symptoms starting on 
               
               
                 ΔguaB SM20 
                   
                 76Sa88 
                   
                   
                   
                 the 9 th  day after infection. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Virulence test in BALB/c mice of the  S. Enteritidis  mutants SM20 and SM21 
               
            
           
           
               
               
               
               
            
               
                 Infection 
                   
                 Day of 
                   
               
            
           
           
               
               
               
               
               
            
               
                 Strain 
                 Dose 
                 Survival 
                 death 
                 State of the mice 
               
               
                   
               
            
           
           
               
            
               
                 First Experiment 
               
            
           
           
               
               
               
               
               
            
               
                 Negative control: not infected 
                 / 
                 11/11 
                 / 
                 Asymptomatic 
               
               
                 Positive control:  S. Enteritidis  76Sa88 
                 2.1 × 10 8   
                 0/5 
                 7, 7, 8, 
                 Severe symptoms from day 5 
               
               
                   
                   
                   
                 8, 9 
                 onwards 
               
               
                   S. Enteritidis  ΔguaB SM20 
                 5.1 × 10 8   
                  9/10 
                 13 
                 Mild to severe symptoms from 
               
               
                   
                   
                   
                   
                 day 7 till day 17 
               
               
                   S. Enteritidis  ΔguaB: ΔfliC SM21 
                 4.3 × 10 8   
                 10/10 
                 / 
                 Asymptomatic 
               
            
           
           
               
            
               
                 Second Experiment 
               
            
           
           
               
               
               
               
               
            
               
                 Negative control: not infected 
                 / 
                 4/4 
                 / 
                 Asymptomatic 
               
               
                 Positive control:  S. Enteritidis  76Sa88 
                 1.4 × 10 8   
                 0/3 
                 8, 9, 9 
                 Severe symptoms from day 6 
               
               
                   
                   
                   
                   
                 onwards 
               
               
                   S. Enteritidis  ΔguaB SM20 
                 1.9 × 10 8   
                 3/3 
                 / 
                 Asymptomatic 
               
               
                   S. Enteritidis  ΔguaB ΔfliC SM21 
                 3.2 × 10 8   
                 3/3 
                 / 
                 Asymptomatic 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Challenge of mice vaccinated with the  S. Enteritidis  mutants SM20 and SM21 
               
            
           
           
               
               
               
               
            
               
                 Vaccination 
                 Challenge 
                   
                 Day of 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Strain 
                 Dose 
                 Strain 
                 Dose 
                 Survival 
                 death 
                 State of the mice 
               
               
                   
               
            
           
           
               
            
               
                 First Experiment 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Negative 
                 / 
                 
                   S. Enteritidis 
                 
                 1.6 × 10 8   
                 0/5 
                 7, 8, 8, 
                 Severe symptoms onwards from 
               
               
                 control: milk 
                   
                 wild type 
                   
                   
                 8, 9 
                 day 6 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 2.1 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.6 × 10 8   
                 / 
                 / 
                 / 
               
               
                 wild type strain 
                   
                 wild type 
               
               
                 76Sa88 
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 5.1 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.6 × 10 8   
                 4/4 
                 / 
                 Asymptomatic 
               
               
                 ΔguaB SM20 
                   
                 wild type 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 4.3 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.6 × 10 8   
                 5/5 
                 / 
                 Asymptomatic 
               
               
                 ΔguaB ΔfliC SM21 
                   
                 wild type 
               
               
                   
                   
                 strain 76Sa88 
               
            
           
           
               
            
               
                 Second Experiment 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Negative 
                 / 
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 0/2 
                 9, 18 
                 Severe symptoms onwards from 
               
               
                 control: milk 
                   
                 wild type 
                   
                   
                   
                 day 6 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 1.4 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 / 
                 / 
                 / 
               
               
                 wild type strain 
                   
                 wild type 
               
               
                 76Sa88 
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 1.9 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 2/3 
                 10 
                 No symptoms, except one with 
               
               
                 ΔguaB SM20 
                   
                 wild type 
                   
                   
                   
                 severe symptoms 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 3.2 × 10 8   
                 
                   S. Enteritidis 
                 
                 1.5 × 10 8   
                 3/3 
                 / 
                 Asymptomatic 
               
               
                 ΔguaB ΔfliC SM21 
                   
                 wild type 
               
               
                   
                   
                 strain 76Sa88 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Virulence test in BALB/c mice of the  S. Enteritidis  mutants 
               
               
                 SM71, SM73 and SM69 
               
            
           
           
               
               
               
               
            
               
                 Infection 
                   
                 Day of 
                   
               
            
           
           
               
               
               
               
               
            
               
                 Strain 
                 Dose 
                 Survival 
                 death 
                 State of the mice 
               
               
                   
               
               
                 Negative control: 
                 / 
                 4/4 
                 / 
                 Asymptomatic 
               
               
                 not infected 
               
               
                 Positive control: 
                 3.7 × 10 8   
                 0/3 
                 7, 8, 9 
                 Severe symptoms 
               
               
                   S. Enteritidis  76Sa88 
                   
                   
                   
                 onwards from 
               
               
                   
                   
                   
                   
                 day 5 
               
               
                 
                   S. Enteritidis 
                 
                 1.4 × 10 8   
                 0/3 
                 6, 8, 8 
                 Severe symptoms 
               
               
                 ΔfliC SM71 
                   
                   
                   
                 onwards from 
               
               
                   
                   
                   
                   
                 day 4 
               
               
                 
                   S. Enteritidis 
                 
                 7.6 × 10 8   
                 5/5 
                 / 
                 Mild symptoms, 
               
               
                 ΔguaB SM69 
                   
                   
                   
                 from day 11 
               
               
                   
                   
                   
                   
                 till day 18 
               
               
                 
                   S. Enteritidis 
                 
                 1.2 × 10 8   
                 5/5 
                 / 
                 Reduced activity, 
               
               
                 ΔguaB ΔfliC SM73 
                   
                   
                   
                 from day 
               
               
                   
                   
                   
                   
                 11 till day 13 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Challenge of mice vaccinated with the  S. Enteritidis  mutants SM71, SM73 and SM69 
               
            
           
           
               
               
               
               
            
               
                 Vaccination 
                 Challenge 
                   
                 Day of 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Strain 
                 Dose 
                 Strain 
                 Dose 
                 Survival 
                 death 
                 State of the mice 
               
               
                   
               
               
                 Negative 
                 / 
                 
                   S. Enteritidis 
                 
                 3.1 × 10 8   
                 0/4 
                 8, 8, 8, 
                 Severe symptoms onwards from 
               
               
                 control: milk 
                   
                 wild type 
                   
                   
                 9 
                 day 5 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 3.7 × 10 8   
                 
                   S. Enteritidis 
                 
                 3.1 × 10 8   
                 / 
                 / 
                 / 
               
               
                 wild type strain 
                   
                 wild type 
               
               
                 76Sa88 
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 1.4 × 10 8   
                 
                   S. Enteritidis 
                 
                 3.1 × 10 8   
                 / 
                 / 
                 / 
               
               
                 ΔfliC SM71 
                   
                 wild type 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 7.6 × 10 8   
                 
                   S. Enteritidis 
                 
                 3.1 × 10 8   
                 2/5 
                 8, 8, 19 
                 Severe symptoms onwards from 
               
               
                 ΔguaB SM69 
                   
                 wild type 
                   
                   
                   
                 day 5 
               
               
                   
                   
                 strain 76Sa88 
               
               
                 
                   S. Enteritidis 
                 
                 1.2 × 10 8   
                   
                   
                 5/5 
                 / 
                 Asymptomatic 
               
               
                 ΔguaB ΔfliC SM73 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Safety evaluation of the  Salmonella  mutant SM69 in one-day-old chickens 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Infection 
                   
                   
                   
                   
                   
                   
               
               
                 Strain 
                 Group 
                 N 
                 Titer 
                 Route 
                 Survival 
                 Day of death (DPI) 
               
               
                   
               
               
                   S. Enteritidis  SM69 
                 1: SM69-IT 
                 10 
                 1.3 × 10 8   
                 intratracheal 
                  4/10* 
                 0, 2, 3, 5, 13 
               
               
                   
                   
                   
                 CFU/0.2 ml 
               
               
                   S. Enteritidis  SM69 
                 2: SM69-OG 
                 10 
                 1.3 × 10 8   
                 oral gavage 
                   8/10** 
                 0, 5 
               
               
                   
                   
                   
                 CFU/0.2 ml 
               
               
                 Negative control: PBS 
                 3: PBS-IT 
                 10 
                 PBS - 0.2 ml 
                 intratracheal 
                 10/10 
                 — 
               
               
                 Negative control: PBS 
                 4: PBS-OG 
                 10 
                 PBS - 0.2 ml 
                 oral gavage 
                 10/10 
                 — 
               
               
                   
               
               
                 IT Intratracheal 
               
               
                 OG Oral gavage 
               
               
                 DPI Days post inoculation 
               
               
                 *In group 1, 1 bird died during inoculation; 1 bird died at 3, 5 and 13 DPI; and 2 birds at 2 DPI respectively 
               
               
                 **In group 2, 1 bird died during inoculation; and 1 bird died at 5 days DPI 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Safety evaluation of the  Salmonella  mutant SM69 in 2-week-old chickens 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 Day of 
                 Mean 
                   
               
               
                 Infection 
                   
                   
                   
                   
                   
                 death 
                 weight 
                 Std 
               
               
                 Strain 
                 Group 
                 N 
                 Titer 
                 Route 
                 Survival 
                 (DPI) 
                 (kg) 
                 weight 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   S. Enteritidis  SM69 
                 1: SM69-IT 
                 10 
                 2.3 × 10 8   
                 IT 
                  9/10* 
                 13 
                 0.429 
                 0.064 
               
               
                   
                   
                   
                 CFU/0.2 ml 
               
               
                   S. Enteritidis  SM69 
                 2: SM69-OG 
                 10 
                 2.3 × 10 8   
                 OG 
                 10/10 
                 — 
                 0.420 
                 0.044 
               
               
                   
                   
                   
                 CFU/0.2 ml 
               
               
                 Vaccine control: Poulvac ® 
                 3: Poulvac-IT 
                 10 
                 2.2 × 10 8   
                 IT 
                 10/10 
                 — 
                 0.423 
                 0.046 
               
               
                 ST* 
                   
                   
                 CFU/0.2 ml 
               
               
                 Negative control: PBS 
                 4: PBS-IT 
                 5 
                 PBS - 0.2 
                 OG 
                 5/5 
                 — 
                 0.388 
                 0.019 
               
               
                   
                   
                   
                 mL 
               
               
                   
               
               
                 IT Intratracheal 
               
               
                 OG Oral gavage 
               
               
                 DPI Days post inoculation 
               
               
                 *Death due to yolk sac infection 
               
               
                 **A live  S. Typhimurium  AroA −  vaccine against  S. Typhimurium   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Virulence experiments with  S. Typhimurium  mutant strains in 
               
               
                 BALB/c mice. Oral inoculation with approximately 10 8  cells 
               
               
                 of the  S. Typhimurium  strain 1491S96 
               
            
           
           
               
               
               
            
               
                 Infection 
                   
                   
               
               
                 Strain 
                 Survival 
               
               
                 ( S. Typhimurium  1491S96) 
                 (day of death) 
                 State of the mice 
               
               
                   
               
               
                 Wild type SM2 
                 0/3 
                 Disease symptoms 
               
               
                   
                 (9, 9, 10) 
                 from day 4 onwards 
               
               
                 ΔfliC SM91 
                 0/5 
                 Disease symptoms 
               
               
                   
                 (9, 10, 11, 15, 15) 
                 from day 5 onwards 
               
               
                 ΔfljBA SM90 
                 0/5 
                 Severe disease symptoms 
               
               
                   
                 (8, 10, 10, 11, 34) 
                 from day 7 onwards 
               
               
                 ΔfljBA ΔfliC SM83 
                 0/5 
                 Severe disease symptoms 
               
               
                   
                 (8, 9, 12, 14, 15) 
                 from day 7 onwards 
               
               
                 ΔguaB SM86 
                  2/5* 
                 Mild disease symptoms 
               
               
                   
                 (2, 2, 2) 
                 from day 9 
               
               
                   
                   
                 until challenge 
               
               
                 ΔguaB ΔfljBA SM87 
                 5/5 
                 No symptoms 
               
               
                 ΔguaB ΔfliC ΔfljBA SM89 
                 5/5 
                 No symptoms 
               
               
                 Control (not infected) 
                 4/4 
                 No symptoms 
               
               
                   
               
               
                 *died after a fight 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Challenge experiments with  S. Typhimurium  mutant strains in BALB/c mice. 
               
               
                 Oral vaccination with approximately 10 8  cells of the  S. Typhimurium   
               
               
                 strain 1491S96 
               
            
           
           
               
               
            
               
                   
                 Challenge 
               
            
           
           
               
               
               
               
               
            
               
                 Vaccination 
                 Strain 
                   
                   
                   
               
               
                 Strain 
                 ( S. Typhimurium   
                 Dose 
                 Survival 
               
               
                 ( S. Typhimurium  1491S96) 
                 1491S96) 
                 (CFU) 
                 (day of death) 
                 State of the mice 
               
               
                   
               
               
                 ΔguaB SM86 
                   S. Typhimurium  1491S96 
                 1.3 × 10 7   
                 2/2 
                 Mild symptoms until days 
               
               
                   
                   
                   
                   
                 14, afterwards one mouse 
               
               
                   
                   
                   
                   
                 showed clear symptoms, the 
               
               
                   
                   
                   
                   
                 other was healthy again 
               
               
                 ΔguaB ΔfljBA SM87 
                   S. Typhimurium  1491S96 
                 1.3 × 10 7   
                 5/5 
                 Reduced activity between 
               
               
                   
                   
                   
                   
                 day 8 and day 10 
               
               
                 ΔguaB ΔfliC ΔfljBA SM89 
                   S. Typhimurium  1491S96 
                 1.3 × 10 7   
                 5/5 
                 Reduced activity between 
               
               
                   
                   
                   
                   
                 day 8 and day 10 
               
               
                 Control (not infected) 
                   S. Typhimurium  1491S96 
                 1.3 × 10 7   
                 0/4 
                 Severe symptoms from day 6 
               
               
                   
                   
                   
                   
                 onwards 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Virulence experiments with  S. Typhimurium  1491S96 
               
               
                 mutant strains in BALB/c mice. 
               
            
           
           
               
               
               
               
            
               
                 Infection 
                   
                   
                   
               
               
                 Strain 
               
               
                 ( S. Typhimurium   
                   
                 Survival 
               
               
                 1491S96) 
                 Dose 
                 (day of death) 
                 State of the mice 
               
               
                   
               
               
                 Wild type SM2 
                 0.8 × 10 8   
                 1/4 
                 Disease symptoms 
               
               
                   
                   
                 (11, 13, 14) 
                 from day 6 onwards 
               
               
                 ΔguaB SM86 
                 0.8 × 10 8   
                 5/5 
                 Weak symptoms 
               
               
                   
                   
                   
                 on day 13 and 14 
               
               
                 ΔguaB ΔfliC SM91 
                 2.5 × 10 8   
                 5/5 
                 No symptoms 
               
               
                 ΔguaB ΔfljBA SM87 
                 1.5 × 10 8   
                 5/5 
                 No symptoms 
               
               
                 ΔguaB ΔfliC 
                 1.7 × 10 8   
                 5/5 
                 No symptoms 
               
               
                 ΔfljBA SM89 
               
               
                 Control (not infected) 
                 — 
                 5/5 
                 No symptoms 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Protection experiments with  S. Typhimurium  1491S96 mutant strains in BALB/c mice. 
               
            
           
           
               
               
               
               
               
               
            
               
                 Vaccination 
                   
                 Challenge 
                   
                 Survival 
                   
               
               
                 Strain 
                   
                 Strain 
                   
                 (day of 
               
               
                 ( S. Typhimurium  1431S96) 
                 Dose 
                 ( S. Typhimurium  1491S96) 
                 Dose 
                 death) 
                 State of the mice 
               
               
                   
               
               
                 ΔguaB SM86 
                 0.8 × 10 8   
                   S. Typhimurium  1491S96 
                 2.7 × 10 8   
                 5/5 
                 Reduced activity 
               
               
                   
                   
                   
                   
                   
                 from day 6 till day 
               
               
                   
                   
                   
                   
                   
                 16 
               
               
                 ΔguaB ΔfliC SM91 
                 2.5 × 10 8   
                   S. Typhimurium  1491S96 
                 2.7 × 10 8   
                 5/5 
                 Reduced activity 
               
               
                   
                   
                   
                   
                   
                 onwards from day 7; 
               
               
                   
                   
                   
                   
                   
                 weak symptoms from 
               
               
                   
                   
                   
                   
                   
                 day 8 untill day 14 
               
               
                 ΔguaB ΔfljBA SM87 
                 1.5 × 10 8   
                   S. Typhimurium  1491S96 
                 2.7 × 10 8   
                 3/5 
                 Weak symptoms 
               
               
                   
                   
                   
                   
                 (10, 28) 
                 between day 6 and 
               
               
                   
                   
                   
                   
                   
                 day 16 
               
               
                 ΔguaB ΔfliC•ΔfljBA SM89 
                 1.7 × 10 8   
                   S. Typhimurium  1491S96 
                 2.7 × 10 8   
                 4/5 
                 Reduced activity 
               
               
                   
                   
                   
                   
                 (19) 
                 between day 8 and 
               
               
                   
                   
                   
                   
                   
                 day 16 
               
               
                 Control (not infected) 
                 — 
                   S. Typhimurium  1491S96 
                 2.7 × 10 8   
                 0/5 
                 Severe symptoms from 
               
               
                   
                   
                   
                   
                 (8, 9, 10, 11, 16) 
                 day 6 onwards