A real-time PCR for the detection of Salmonella Enteritidis in poultry meat and consumption eggs

A robust duplex 5' nuclease (TaqMan) real-time PCR was developed and in-house validated for the specific detection of Salmonella enterica subspecies enterica serovar Enteritidis in whole chicken carcass rinses and consumption eggs. The assay uses specifically designed primers and a TaqMan probe to target the Prot6e gene located on the S. Enteritidis specific 60-kb virulence plasmid. As an internal amplification control to monitor Salmonella DNA in the sample, a second primer/TaqMan probe set detects simultaneously the Salmonella specific invA gene. The assay identified correctly 95% of the 79 Salmonella Enteritidis strains tested comprising 19 different phage types. None of the 119 non-Enteritidis strains comprising 54 serovars was positive for the Prot6e gene. The assay detection probability was for 10(2) or more genome equivalents 100% and for 10 equivalents 83%. A pre-PCR sample preparation protocol including a pre-enrichment step in buffered peptone water, followed by DNA extraction was applied on low levels of artificially contaminated whole chicken carcass rinses and eggs from hens as well as 25 potentially naturally contaminated chickens. The detection limit was less than three CFU per 50 ml carcass rinse or 10 ml egg. The sensitivity and specificity compared to the traditional culture-based detection method and serotyping were both 100%. Twenty-five potentially naturally contaminated chickens were compared by the real-time PCR and the traditional cultural isolation method resulting in four Salmonella positive samples of which two were positive for the Prot6e gene and serotyped as S. Enteritidis. We show also that Salmonella isolates which have a rough lipopolysaccharide structure could be assigned to the serovar Enteritidis by the real-time PCR. This methodology can contribute to meet the need of fast identification and detection methods for use in monitoring and control measures programmes.     

Identification of genes associated with survival of Salmonella enterica serovar Enteritidis in chicken egg albumen

Salmonella enterica consists of over 2,000 serovars that are major causes of morbidity and mortality associated with contaminated food. Despite similarities among serovars of Salmonella enterica, many demonstrate unique host specificities, epidemiological characteristics, and clinical manifestations. One of the unique epidemiological characteristics of the serovar Enteritidis is that it is the only bacterium routinely transmitted to humans through intact chicken eggs. Therefore, Salmonella enterica serovar Enteritidis must be able to persist inside chicken eggs to be transmitted to humans, and its survival in egg is important for its transmission to the human population. The ability of Salmonella enterica serovar Enteritidis to survive in and transmit through eggs may have contributed to its drastically increased prevalence in the 1980s and 1990s. In the present study, using transposon-mediated mutagenesis, we have identified genes important for the association of Salmonella enterica serovar Enteritidis with chicken eggs. Our results indicate that genes involved in cell wall structural and functional integrity, and nucleic acid and amino acid metabolism are important for Salmonella enterica serovar Enteritidis to persist in egg albumen. Two regions unique to Salmonella enterica serovar Enteritidis were also identified, one of which enhanced the survival of a Salmonella enterica serovar Typhimurium isolate in egg albumen. The implication of our results to the serovar specificity of Salmonella enterica is also explored in the present study.     

Salmonella carrier state in chicken: comparison of expression of immune response genes between susceptible and resistant animals

Asymptomatic Salmonella enterica serovar Enteritidis carrier state in poultry has serious consequences on food safety and public health due to the risks of food poisoning following consumption of contaminated products. An understanding the mechanisms of persistence of Salmonella in the digestive tract of chicken can be achieved by a better knowledge of the defects in the control of infection in susceptible versus resistant animals. The gene expression of innate immune response factors including anti-microbial molecules, inflammatory and anti-infectious cytokines was studied in the caecal lymphoid tissue associated with the carrier state. Expression levels of these genes were assessed by real-time PCR and were compared in two inbred lines of chickens differing in resistance to the carrier state following oral inoculation of S. enterica serovar Enteritidis at 1 week of age. No correlation was observed between resistance/susceptibility to caecal carrier state and level of interleukin (IL)-1beta, IL-8, IL-18, inducible NO synthase (iNOS) and natural resistance associated macrophage protein 1 (NRAMP1). A high baseline level of defensin gene expression was recorded in young animals from the susceptible line. In contrast, a significantly low expression of interferon-gamma (IFN-gamma) gene was observed in these susceptible infected animals in comparison to resistant ones and healthy counterparts. IFN-gamma expression level represents a valuable indication of immunodeficiency associated with persistence of Salmonella in the chicken digestive tract, and IFN-gamma thus represents a factor to consider in the development of prophylactic measures for the reduction of Salmonella carrier state.     

Complete genomic sequence of Salmonella enterica serovar Enteritidis phage SE2

Salmonella enterica serovar Enteritidis has remained a major food-borne pathogen in humans. We isolated a virulent S. enterica serovar Enteritidis bacteriophage, SE2, which belongs to the family Siphoviridae. Phage SE2 could lyse S. enterica serovar Enteritidis PT-4, and its virulence was maintained even at ambient temperature. The genomic sequence of phage SE2 was composed of 43,221 bp with close similarity to those of Salmonella phage SETP3 and Salmonella phage SS3e. The strong and stable lytic activity of this phage might enable its use as a therapeutic or biocontrol agent against S. enterica serovar Enteritidis.     

Identification by subtractive hybridization of sequences specific for Salmonella enterica serovar enteritidis.

Salmonella enterica serovar Enteritidis, a major cause of food poisoning, can be transmitted to humans through intact chicken eggs when the contents have not been thoroughly cooked. Infection in chickens is asymptomatic; therefore, simple, sensitive, and specific detection methods are crucial for efforts to limit human exposure. Suppression subtractive hybridization was used to isolate DNA restriction fragments present in Salmonella serovar Enteritidis but absent in other bacteria found in poultry environments. Oligonucleotide primers to candidate regions were used in polymerase chain reactions to test 73 non-Enteritidis S. enterica isolates comprising 34 different serovars, including Dublin and Pullorum, two very close relatives of Enteritidis. A primer pair to one Salmonella difference fragment (termed Sdf I) clearly distinguished serovar Enteritidis from all other serovars tested, while two other primer pairs only identified a few non-Enteritidis strains. These primer pairs were also useful for the detection of a diverse collection of clinical and environmental Salmonella serovar Enteritidis isolates. In addition, five bacterial genera commonly found with Salmonella serovar Enteritidis were not detected. By treating total DNA with an exonuclease that degrades sheared chromosomal DNA but not intact circular plasmid DNA, it was shown that Sdf I is located on the chromosome. The Sdf I primers were used to screen a Salmonella serovar Enteritidis genomic library and a unique 4,060-bp region was defined. These results provide a basis for developing a rapid, sensitive, and highly specific detection system for Salmonella serovar Enteritidis and provide sequence information that may be relevant to the unique characteristics of this serovar.     

A novel multiplex PCR assay for the detection of Salmonella enterica serovar Enteritidis in human faeces

AIMS: To develop a multiplex PCR assay for the detection of Salmonella enterica serovar Enteritidis in human faeces. METHODS AND RESULTS: A total of 54 Salmonella strains representing 19 serovars and non-Salmonella strains representing 11 different genera were used. Five primer pairs were employed in the assay. Three of them targeted to the genes hilA, spvA and invA that encode virulence-associated factors. A fourth primer pair amplified a fragment of a unique sequence within S. enterica serovar Enteritidis genomes. An internal amplification control (a fragment of a conservative sequence within the 16S rRNA genes) was targeted by a fifth primer pair. The assay produced two or three amplicons from the invA, hilA and 16S rRNA genes for 19 Salmonella serovars. All Salmonella and non-Salmonella strains yielded a band of an internal amplification control. For S. enterica serovar Typhimurium, four products (the fourth from the spvA gene), and for S. enterica serovar Enteritidis five amplicons (the fifth from the sdf gene) were observed. S. enterica serovar Enteritidis was cultured from three of 71 rectal swabs from diarrhoeal patients. Five specific amplicons were generated with the multiplex PCR assay only from culture-positive faecal samples. CONCLUSION: The multiplex PCR assay specifically detects S. enterica serovar Enteritidis. SIGNIFICANCE AND IMPACT OF THE STUDY: This is a novel multiplex PCR assay, which contains an internal amplification control and enables concurrent survey for Salmonella virulence genes.     

Shedding light on Salmonella carriers

Host-to-host transmission in most Salmonella serovars occurs primarily via the fecal-oral route. Salmonella enterica serovar Typhi is a human host-adapted pathogen and some S. Typhi patients become asymptomatic carriers. These individuals excrete large numbers of the bacteria in their feces and transmit the pathogen by contaminating water or food sources. The carrier state has also been described in livestock animals and is responsible for food-borne epidemics. Identification and treatment of carriers are crucial for the control of disease outbreaks. In this review, we describe recent advances in molecular profiling of human carriers and the use of animal models to identify potential host and bacterial genes involved in the establishment of the carrier state.     

Features of Salmonella serovars among food handlers in Kyushu, Japan

Salmonella were isolated from 106 (0.032%) of 331,644 fecal samples from food handlers, and from 144 of 11,478 fecal samples from symptomatic patients in Japan to determine the incidence and features of Salmonella serovars among food handlers. S. enterica subspecies enterica serovar Infantis (S. serovar Infantis) was the dominant serovar (accounting for 48.1%), followed by S. serovar Corvallis, which showed poor genetic diversity, and S. serovar Enteritidis among food handlers. The former two serovars were not dominant among symptomatic patients. The present study demonstrates the need for education on the sanitary handling of chicken eggs and chicken meat, which are possible infectious sources of these Salmonella serovars.     

Epidemiological analysis of Salmonella enterica ssp. enterica serovars Hadar, Brancaster and Enteritidis from humans and broiler chickens in Senegal using pulsed-field gel electrophoresis and antibiotic susceptibility

AIMS: Salmonella Hadar, Salmonella Brancaster and Salmonella Enteritidis are the main Salmonella enterica ssp. enterica serovars isolated from poultry in Senegal. Our objective was to analyse the pulsed-field gel electrophoresis (PFGE) and antibioresistance patterns of strains belonging to these serovars and to assess the significance of broiler-chicken meat as a source of human infection. METHODS AND RESULTS: A total of 142 Salmonella isolates were analysed: 79 were isolated from Senegalese patients with sporadic diarrhoea (11 S. Hadar, nine S. Brancaster and 59 S. Enteritidis) and 63 from poultry (30 S. Hadar, 17 S. Brancaster and 16 S. Enteritidis). The PFGE of XbaI- and SpeI-digested chromosomal DNA gave 20 distinct profiles for S. Hadar, nine for S. Brancaster and 22 for S. Enteritidis. Each serovar was characterized by a major pulsotype which was X3S1 in 42% of S. Hadar, X8S1 in 53.8% of S. Brancaster and X1S2 in 43% of S. Enteritidis isolates. Human and poultry isolates of Salmonella had common PFGE patterns. Antibiosensitivity tests showed multiresistance (more than two drugs) was encountered in 14.5% of S. Hadar and in 5% of S. Enteritidis isolates. Resistance to quinolones was considered to be of particular importance and 14.5% of S. Hadar isolates were found to be resistant to nalidixic acid. CONLCUSIONS: The sharing of similar PFGE profiles among isolates from humans and poultry provided indirect evidence of Salmonella transmission from contaminated broiler meat. But most of the Salmonella isolates remained drug sensitive. SIGNIFICANCE AND IMPACT OF THE STUDY: Efforts are needed to eliminate Salmonella from poultry meat intended for human consumption. This study has also highlighted the importance of continuous surveillance to monitor antimicrobial resistance in bacteria associated with animals and humans.     

Development of liposome immunoassay for salmonella spp. using immunomagnetic separation and immunoliposome

The ability to detect Salmonella spp. is essential in the prevention of foodborne illness. This study examined a Salmonella spp. detection method involving the application of immunomagnetic separation and immunoliposomes (IMS/IL) encapsulating sulforhodamine B (SRB), a fluorescent dye. A quantitative assay was conducted by measuring the fluorescence intensity of SRB that was produced from an immunomagnetic bead-Salmonella spp.-immunoliposome complex. The results indicated detection limits of 2.7x10(5) and 5.2x10(3) CFU/ml for Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) and Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium), respectivley. The signal/noise ratio was improved by using 4% skim milk as a wash solution rather than 2% BSA. In addition, higher fluorescence intensity was obtained by increasing the liposome size. Compared with the conventional plating method, which takes 3-4 days for the isolation and identification of Salmonella spp., the total assay time of 10 h only including 6 h of culture enrichment was necessary for the Salmonella detection by IMS/IL. These results indicate that the IMS/ IL has great potential as an alternative rapid method for Salmonella detection.     

Real-time monitoring of Salmonella enterica in free-range geese

Free-range geese were sampled longitudinally and Salmonella isolates characterized to reveal highly diverging colonization dynamics. One flock was intermittently colonized with one strain of Salmonella enterica serovar Enteritidis from 2 weeks of age, while in another, S. enterica serovar Mbandaka appeared after 9 weeks, without dissemination but with multiple serovars appearing at later stages.     

Excision of an unstable pathogenicity island in Salmonella enterica serovar Enteritidis is induced during infection of phagocytic cells

The availability of the complete genome sequence of several Salmonella enterica serovars has revealed the presence of unstable genetic elements in these bacteria, such as pathogenicity islands and prophages. This is the case of Salmonella enterica serovar Enteritidis (S. Enteritidis), a bacterium that causes gastroenteritis in humans and systemic infection in mice. The whole genome sequence analysis for S. Enteritidis unveiled the presence of several genetic regions that are absent in other Salmonella serovars. These regions have been denominated "regions of difference" (ROD). In this study we show that ROD21, one of such regions, behaves as an unstable pathogenicity island. We observed that ROD21 undergoes spontaneous excision by two independent recombination events, either under laboratory growth conditions or during infection of murine cells. Importantly, we also found that one type of excision occurred at higher rates when S. Enteritidis was residing inside murine phagocytic cells. These data suggest that ROD21 is an unstable pathogenicity island, whose frequency of excision depends on the environmental conditions found inside phagocytic cells.     

Effect of the Salmonella pathogenicity island 2 type III secretion system on Salmonella survival in activated chicken macrophage-like HD11 cells

In order to better identify the role of the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (T3SS) in chickens, we used the well-known gentamicin protection assay with activated HD11 cells. HD11 cells are a macrophage-like chicken cell line that can be stimulated with phorbol 12-myristate 13-acetate (PMA) to exhibit more macrophage-like morphology and greater production of reactive oxygen species (ROS). Activated HD11 cells were infected with a wild-type Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) strain, a SPI-2 mutant S. Typhimurium strain, a wild-type Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) strain, a SPI-2 mutant S. Enteritidis strain, or a non-pathogenic Escherichia coli (E. coli) strain. SPI-2 mutant strains were found to survive as well as their parent strain at all time points post-uptake (PU) by the HD11 cells, up to 24 h PU, while the E. coli strain was no longer recoverable by 3 h PU. We can conclude from these observations that the SPI-2 T3SS of S. Typhimurium and S. Enteritidis is not important for survival of Salmonella in the activated macrophage-like HD11 cell line, and that Salmonella must employ other mechanisms for survival in this environment, as E. coli is effectively eliminated.     

Differences in gene content between Salmonella enterica serovar Enteritidis isolates and comparison to closely related serovars Gallinarum and Dublin

Salmonella enterica serovar Enteritidis is often transmitted into the human food supply through eggs of hens that appear healthy. This pathogen became far more prevalent in poultry following eradication of the fowl pathogen S. enterica serovar Gallinarum in the mid-20th century. To investigate whether changes in serovar Enteritidis gene content contributed to this increased prevalence, and to evaluate genetic heterogeneity within the serovar, comparative genomic hybridization was performed on eight 60-year-old and nineteen 10- to 20-year-old serovar Enteritidis strains from various hosts, using a Salmonella-specific microarray. Overall, almost all the serovar Enteritidis genomes were very similar to each other. Excluding two rare strains classified as serovar Enteritidis in the Salmonella reference collection B, only eleven regions of the serovar Enteritidis phage type 4 (PT4) chromosome (sequenced at the Sanger Center) were absent or divergent in any of the other serovar Enteritidis strains tested. The more recent isolates did not have consistent differences from 60-year-old field isolates, suggesting that no large genomic additions on a whole-gene scale were needed for serovar Enteritidis to become more prevalent in domestic fowl. Cross-hybridization of phage genes on the array with related genes in the examined genomes grouped the serovar Enteritidis isolates into two major lineages. Microarray comparisons of the sequenced serovar Enteritidis PT4 to isolates of the closely related serovars Dublin and Gallinarum (biovars Gallinarum and Pullorum) revealed several genomic areas that distinguished them from serovar Enteritidis and from each other. These differences in gene content could be useful in DNA-based typing and in understanding the different phenotypes of these related serovars.     

Lack of clonal relationship between non-typhi Salmonella strain types from humans and those isolated from animals living in close contact

Antibiogram patterns and chromosomal DNA typing were used to compare 151 non-typhoidal Salmonella spp. (NTS) isolated from patients and 78 from animals, environmental or food specimens obtained within or near the homes of patients with invasive salmonellosis. The majority of NTS from humans (137; 90.7%) were Salmonella enterica serotype Typhimurium (S. Typhimurium) and S. Enteritidis. Chicken specimens and feeds produced (24; 52.2%) S. Enteritidis, while S. Agona was the predominant (20; 77%) serovar among pigs and dairy cows. The majority (97; 64.2%) of NTS from humans were multidrug resistant, while NTS from cows, pigs, beef carcass swabs and sewers were fully susceptible to all antibiotics tested. Pulsed-field gel electrophoresis patterns of XbaI-digested genomic DNA of NTS from the humans and the chickens were different. However, S. Enteritidis from chickens, and S. Braenderup and S. Agona from cows and pigs were clustered together in one group. There was no significant relatedness between NTS isolates from humans and those from animals, food or the environment in close contact to humans.     

Uptake and replication of Salmonella enterica in Acanthamoeba rhysodes

The ability of salmonellae to become internalized and to survive and replicate in amoebae was evaluated by using three separate serovars of Salmonella enterica and five different isolates of axenic Acanthamoeba spp. In gentamicin protection assays, Salmonella enterica serovar Dublin was internalized more efficiently than Salmonella enterica serovar Enteritidis or Salmonella enterica serovar Typhimurium in all of the amoeba isolates tested. The bacteria appeared to be most efficiently internalized by Acanthamoeba rhysodes. Variations in bacterial growth conditions affected internalization efficiency, but this effect was not altered by inactivation of hilA, a key regulator in the expression of the invasion-associated Salmonella pathogenicity island 1. Microscopy of infected A. rhysodes revealed that S. enterica resided within vacuoles. Prolonged incubation resulted in a loss of intracellular bacteria associated with morphological changes and loss of amoebae. In part, these alterations were associated with hilA and the Salmonella virulence plasmid. The data show that Acanthamoeba spp. can differentiate between different serovars of salmonellae and that internalization is associated with cytotoxic effects mediated by defined Salmonella virulence loci.     

Lipopolysaccharide O-chain microheterogeneity of Salmonella serotypes Enteritidis and Typhimurium

Variability in the lipopolysaccharide (LPS) of the two most prevalent Salmonella serotypes causing food-borne salmonellosis was assessed using gas chromatography analysis of neutral sugars from 43 Salmonella enterica serovar Enteritidis ( S . Enteritidis) and 20 Salmonella enterica serovar Typhimurium ( S . Typhimurium) isolates . Four substantially different types of O-chain chemotypes were detected using cluster analysis of sugar compositions; these were low-molecular-mass (LMM) LPS, glucosylated LMM LPS, high-molecular-mass (HMM) LPS and glucosylated HMM LPS. Nineteen out of 20 S . Typhimurium isolates yielded glucosylated LMM . In contrast, S . Enteritidis produced a more diverse structure, which varied according to the source and history of the isolate: 45.5% of egg isolates yielded glucosylated HMM LPS; 100% of stored strains lacked glucosylation but retained chain length in some cases; and 83.3% of fresh isolates from the naturally infected house mouse Mus musculus produced glucosylated LMM LPS. A chain length determinant ( wzz ) mutant of S . Enteritidis produced a structure similar to that of S . Typhimurium and was used to define what constituted significant differences in structure using cluster analysis. Fine mapping of the S . Enteritidis chromosome by means of a two-restriction enzyme-ribotyping technique suggested that mouse isolates producing glucosylated LMM LPS were closely related to orally invasive strains obtained from eggs, and that stored strains were accumulating genetic changes that correlated with suppression of LPS O-chain glucosylation. These results suggest that the determination of LPS chemotype is a useful tool for epidemiological monitoring of S . Enteritidis , which displays an unusual degree of diversity in its LPS O-chain.     

Survival and filamentation of Salmonella enterica serovar enteritidis PT4 and Salmonella enterica serovar typhimurium DT104 at low water activity

In this study we investigated the long-term survival of and morphological changes in Salmonella strains at low water activity (a(w)). Salmonella enterica serovar Enteritidis PT4 and Salmonella enterica serovar Typhimurium DT104 survived at low a(w) for long periods, but minimum humectant concentrations of 8% NaCl (a(w), 0. 95), 96% sucrose (a(w), 0.94), and 32% glycerol (a(w), 0.92) were bactericidal under most conditions. Salmonella rpoS mutants were usually more sensitive to bactericidal levels of NaCl, sucrose, and glycerol. At a lethal a(w), incubation at 37 degrees C resulted in more rapid loss of viability than incubation at 21 degrees C. At a(w) values of 0.93 to 0.98, strains of S. enterica serovar Enteritidis and S. enterica serovar Typhimurium formed filaments, some of which were at least 200 microm long. Filamentation was independent of rpoS expression. When the preparations were returned to high-a(w) conditions, the filaments formed septa, and division was complete within approximately 2 to 3 h. The variable survival of Salmonella strains at low a(w) highlights the importance of strain choice when researchers produce modelling data to simulate worst-case scenarios or conduct risk assessments based on laboratory data. The continued increase in Salmonella biomass at low a(w) (without a concomitant increase in microbial count) would not have been detected by traditional microbiological enumeration tests if the tests had been performed immediately after low-a(w) storage. If Salmonella strains form filaments in food products that have low a(w) values (0.92 to 0.98), there are significant implications for public health and for designing methods for microbiological monitoring.     

Isolation of Salmonella enterica serovar Enteritidis from houseflies (Musca domestica) found in rooms containing Salmonella serovar Enteritidis-challenged hens

Houseflies (Musca domestica) released into rooms containing hens challenged with Salmonella enterica serovar Enteritidis (Salmonella serovar Enteritidis) rapidly became contaminated with Salmonella serovar Enteritidis. Forty to 50% of the flies were contaminated at 48 h, and the percentage increased to 50 to 70% at 4 and 7 days postexposure and then decreased to 30% at day 15. Initial attempts at recovering surface organisms for culture using an aqueous rinse were largely unsuccessful, while cultures of internal contents readily recovered Salmonella serovar Enteritidis. However, when 0.5% detergent was incorporated into the rinse, high recovery levels of bacteria were observed from both external and internal culture regimens, indicating equal distribution of the organism on and in the fly and a tighter interaction of the organism with the host than previously thought. Salmonella serovar Enteritidis was isolated routinely from the fly gut, on rare occasions from the crop, and never from the salivary gland. Feeding contaminated flies to hens resulted in gut colonization of a third of the birds, but release of contaminated flies in a room containing previously unchallenged hens failed to result in colonization of any of the subject birds. These results indicate that flies exposed to an environment containing Salmonella serovar Enteritidis can become colonized with the organism and might serve as a source for transmission of Salmonella serovar Enteritidis within a flock situation.     

Heterogeneity of persistence of Salmonella enterica serotype Senftenberg strains could explain the emergence of this serotype in poultry flocks

Salmonella enterica serotype Senftenberg (S. Senftenberg) has recently become more frequent in poultry flocks. Moreover some strains have been implicated in severe clinical cases. To explain the causes of this emergence in farm animals, 134 S. Senftenberg isolates from hatcheries, poultry farms and human clinical cases were analyzed. Persistent and non-persistent strains were identified in chicks. The non-persistent strains disappeared from ceca a few weeks post inoculation. This lack of persistence could be related to the disappearance of this serotype from poultry farms in the past. In contrast, persistent S. Senftenberg strains induced an intestinal asymptomatic carrier state in chicks similar to S. Enteritidis, but a weaker systemic infection than S. Enteritidis in chicks and mice. An in vitro analysis showed that the low infectivity of S. Senftenberg is in part related to its low capacity to invade enterocytes and thus to translocate the intestinal barrier. The higher capacity of persistent than non-persistent strains to colonize and persist in the ceca of chickens could explain the increased persistence of S. Senftenberg in poultry flocks. This trait might thus present a human health risk as these bacteria could be present in animals before slaughter and during food processing.