Yersinia Enterocolitica Strains Research Articles

Complete genome sequence of bacteriophage vB_YenP_AP5 which infects Yersinia enterocolitica of serotype O:3.

BackgroundBacteriophage vB_YenP_AP5 is a lytic bacteriophage capable of infecting Yersinia enterocolitica strains of serotype O:3, an epidemiologically significant serotype within this bacterial species that causes yersiniosis in humans. This work describes the complete genome sequence of this phage.ResultsThe genome consists of linear double-stranded DNA of 38,646 bp, with direct terminal repeats of 235 bp in length, and a GC content of 50.7%. There are 45 open reading frames which occupy 89.9% of the genome. Most of the proteins encoded by this virus exhibit sequence similarity to Yersinia phage φYeO3-12 and Salmonella phage φSG-JL2 proteins.ConclusionsGenomic and morphological analyses place the bacteriophage vB_YenP_AP5 in the T7likevirus genus of the subfamily Autographivirinae within the family Podoviridae.

A novel high-resolution melting analysis-based method for Yersinia enterocolitica genotyping

Pathogenic Yersinia enterocolitica strains are associated with biotypes 1B, 2-5, while environmental strains with biotype 1A. In this work a method for Y. enterocolitica genotyping based on HRMA to determine SNPs was developed and the genetic diversity of 50 strains was determined. The strains were clustered into three groups consistent with the pathogenic profile of each biotype. The results provided a better understanding of the Y. enterocolitica genetic variability.

Enhanced Mid-Infrared Chemical Imaging (IRCI) Detection of DNA Microarrays

We report on the optimization of a recently proposed mid-infrared chemical imaging (IRCI) detection method for the analysis of DNA microarrays. The improved protocol allowed for a ten-fold reduction in the time needed to generate a mosaic image of an entire microarray and the production of IR images with high contrast that would facilitate data analysis and interpretation. Advantages of using this protocol were evaluated by applying it to the analysis of four virulence genes in the genomes of 19 strains of the food bacterial pathogen Yersinia enterocolitica.

Analysis of the variation and changes of Yersinia enterocolitica in Ningxia area from 1984 to 2011

To analyze the genetic evolution and bacterial type changes of Yersinia enterocolitica in the Ningxia area between year 1984 and 2011. A total of 296 strains of Yersinia enterocolitica was collected from diarrhea patients, pig, rodents, sheep and dogs between year 1984 and 2011. The serotype, biotype, ail, ystA, ystB, yadA, virF and other toxic genes were detected. The PFGE subtypes of serotype O:3 and O:9 strains and the cluster features were analyzed. Out of 296 Yersinia enterocolitica strains, pig was the main host, accounting for 65.20% (193/296), followed by rodents, accounting for 32.43% (96/296). Serotype and biotype had their own respective dominant types in different periods. During 1984 and 1985, 2 strains of serotype O:3 and 3 strains of serotype O:9 were isolated, all belonged to biotype 3. Because of lack of strains, there were no obvious dominant types found. Between 1997 and 1999, 177 strains of serotype O:9 Yersinia enterocolitica were isolated as the dominant strain; and there were 178 strains of biotype 2 Yersinia enterocolitica were found. During 2007 and 2011, 54 strains of serotype O:3 Yersinia enterocolitica were isolated as dominant strain; followed by 26 strains of serotype O:5. There were separately 44 and 59 strains of biotype 1A and biotype 3. The PCR test divided the 248 strains into 4 types, including pathogenic strains as type I (ail(+), ystA(+), ystB(-), yadA(+), virF(+)). The PFGE divided the serotype O:3 into 12 types, in which K6GN11C30021 and K6GN11C30012 were the dominant types, accounting for 63.64% (42/66). The serotype O:9 were divided into 14 types, in which K6GN11C90010, K6GN11C90008, K6GN11C30018 and K6GN11C90003 were the dominant types, accounting for 89.01% (162/182). The different serotypes of isolated strains in Ningxia district showed different dominant bacteria in different periods; while the biotypes also changed with serotypes. The Yersinia enterocolitica isolated from different years showed great variation.

Tracing genomic variations in two highly virulent Yersinia enterocolitica strains with unequal ability to compete for host colonization

BackgroundYersinia enterocolitica is a gastrointestinal foodborne pathogen found worldwide and which especially affects infants and young children. While different bioserotypes have been associated with varying pathogenicity, research on Y. enterocolitica is mainly conducted on the highly virulent mouse-lethal strains of biotype 1B and serotype O:8. We demonstrate here that two Y. enterocolitica bioserotype 1B/O:8 strains, 8081 and WA-314, display different virulence and fitness properties in a mouse model. In vivo co-infection experiments revealed that strain WA-314 overcomes strain 8081 in the colonization of spleen and liver. To trace the reasons of this incongruity, we present here the first high-quality sequence of the whole genome of strain WA-314 and compare it to the published genome of strain 8081.ResultsRegions previously accepted as unique to strain 8081, like the YAPI and YGI-3 genomic islands, are absent from strain WA-314, confirming their strain-specificity. On the other hand, some fitness- and bacterial competition-associated features, such as a putative colicin cluster and a xenobiotic-acyltransferase-encoding gene, are unique to strain WA-314. Additional acquisitions of strain WA-314 are seven prophage-like regions. One of these prophages, the 28-kb P4-like prophage YWA-4, encodes a PilV-like protein that may be used for adhesion to and invasion of the intestinal cells. Furthermore, a putative autotransporter and two type 1 fimbrial proteins of strain WA-314 show a sequence similarity <50% with the orthologous proteins in strain 8081. The dissimilar sequences of these proteins indicate possible different functions or interaction modes, reflecting the specific adhesion properties of Y. enterocolitica strains 8081 and WA-314 and thus the different efficiency of host colonization. Further important differences were found in two pYV plasmid-encoded virulence factors, YopM and YscP. The impact of these differences on virulence is discussed.ConclusionsOur study emphasizes that the virulence of pathogens can be increased, by acquiring new genes and/or improving the function of essential virulence proteins, resulting in permanently hyper-virulent strains. This work also highlights the importance of addressing genetic and phenotypic variations among closely related bacterial strains, even those belonging to the same bioserotype.

Evaluation of a Single Procedure Allowing the Isolation of Enteropathogenic Yersinia along with Other Bacterial Enteropathogens from Human Stools

Enteropathogenic Yersinia are among the most frequent agents of human diarrhea in temperate and cold countries. However, the incidence of yersiniosis is largely underestimated because of the peculiar growth characteristics of pathogenic Yersinia, which make their isolation from poly-contaminated samples difficult. The use of specific procedures for Yersinia isolation is required, but is expensive and time consuming, and therefore is not systematically performed in clinical pathology laboratories. A means to circumvent this problem would be to use a single procedure for the isolation of all bacterial enteropathogens. Since the Statens Serum Institut enteric medium (SSI) has been reported to allow the growth at 37°C of most Gram-negative bacteria, including Yersinia, our study aimed at evaluating its performances for Yersinia isolation, as compared to the commonly used Yersinia-specific semi-selective Cefsulodin-Irgasan-Novobiocin medium (CIN) incubated at 28°C. Our results show that Yersinia pseudotuberculosis growth was strongly inhibited on SSI at 37°C, and therefore that this medium is not suitable for the isolation of this species. All Yersinia enterocolitica strains tested grew on SSI, while some non-pathogenic Yersinia species were inhibited. The morphology of Y. enterocolitica colonies on SSI allowed their differentiation from various other Gram-negative bacteria commonly isolated from stool samples. However, in artificially contaminated human stools, the recovery of Y. enterocolitica colonies on SSI at 37°C was difficult and was 3 logs less sensitive than on CIN at 28°C. Therefore, despite its limitations, the use of a specific procedure (CIN incubated at 28°C) is still required for an efficient isolation of enteropathogenic Yersinia from stools.

Fate of Yersinia enterocolitica during manufacture, ripening and storage of Lighvan cheese

This study aimed to evaluate the behavior of virulent Yersinia enterocolitica (YE) during the manufacture, ripening and storage of Lighvan cheese with particular reference to strains of YE, initial inoculation level, and storage time. Three strains of YE with low (1logcfu/ml) and high (3logcfu/ml) inoculation levels were inoculated to raw whole ewe's milk which was then used for manufacturing of Lighvan cheese. Throughout the manufacturing, ripening and storage periods the number of YE was counted on selective media. Enumerated colonies were then confirmed by duplex PCR using ail and virF genes. Moreover, some microbial and physiochemical characteristics of the cheese samples were examined. According to the results, initial inoculation level and storage time had statistically significant (P<0.01) effects on persistency of YE, while strain type exhibited no statistically significant (P>0.01) impact on survival of the pathogen. Results showed a rapid increase in the number of YE during manufacturing, however, in the ripening and storage periods the number of YE was decreased and eventually it was eliminated in all cheese batches after 4months of storage.

BOD beads – a ready to use seeding material for estimation of organic load of wastewater

A reusable immobilized microbial composition is designed to estimate the biochemical oxygen demand in industrial wastewater streams. The formulated microbial composition comprises a synergistic mixture of the bacterial strains of Enterobacter cloacae (ATCC no. 29893), Citrobacter amalonaticus (ATCC no. 25406), Pseudomonas aeruginosa (ATCC no. 49622), Yersinia enterocolitica (ATCC no. 27739), Klebsiella oxytoca (ATCC no. 15764), Enterobacter sakazakii (ATCC no. 12868) and Serratia liquefaciens (ATCC no. 25641). The consortium is immobilized by using 2% sodium alginate and 0.15 M calcium chloride to form beads. The said beads are tested as a microbial seeding material for BOD analysis using glucose–glutamic Acid (GGA) as a reference standard. The obtained BOD values were comparable with the values obtained by using sewage as the seeding material. Simultaneously the beads were tested on several synthetic samples as well as industrial effluents. The formulated microbial beads are a ready to use as well as reusable seeding material in BOD analysis. The said beads can be reused up to 5 times with the same efficacy.

Cluster analysis of host cytokine responses to biodefense pathogens in a whole blood ex vivo exposure model (WEEM)

BackgroundRapid detection and therapeutic intervention for infectious and emerging diseases is a major scientific goal in biodefense and public health. Toward this end, cytokine profiles in human blood were investigated using a human whole blood ex vivo exposure model, called WEEM.ResultsSamples of whole blood from healthy volunteers were incubated with seven pathogens including Yersinia pseudotuberculosis, Yersinia enterocolitica, Bacillus anthracis, and multiple strains of Yersinia pestis, and multiplexed protein expression profiling was conducted on supernatants of these cultures with an antibody array to detect 30 cytokines simultaneously. Levels of 8 cytokines, IL-1α, IL-1β, IL-6, IL-8, IL-10, IP-10, MCP-1 and TNFα, were significantly up-regulated in plasma after bacterial exposures of 4 hours. Statistical clustering was applied to group the pathogens based on the host response protein expression profiles. The nearest phylogenetic neighbors clustered more closely than the more distant pathogens, and all seven pathogens were clearly differentiated from the unexposed control. In addition, the Y. pestis and Yersinia near neighbors were differentiated from the B. anthracis strains.ConclusionsCluster analysis, based on host response cytokine profiles, indicates that distinct patterns of immunomodulatory proteins are induced by the different pathogen exposures and these patterns may enable further development into biomarkers for diagnosing pathogen exposure.

Antimicrobial Susceptibility and Distribution of β-Lactamase A (blaA) and β-Lactamase B (blaB) Genes in Enteropathogenic Yersinia Species

One hundred eighty-six strains of enteropathogenic Yersinia (Y.) enterocolitica of bioserotypes 2/O:5,27, 2/O:9, 3/O:3, and 4/O:3 and 12 strains of Yersinia pseudotuberculosis of bioserotypes 1/O:1, 1/O:2, and 2/O:1 from different human (feces) and nonhuman (pig, pork, wild boar, monkey, chinchilla, mara, capybara, salad) sources collected in the years 1995-2009 were examined. Antimicrobial resistance patterns for 12 antimicrobial agents were generated using broth microdilution. The presence and characterization of the β-lactamase genes blaA and blaB were studied using polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (RFLP), respectively. The expression of β-lactamase BlaA and BlaB was detected using double-disc diffusion. Y. enterocolitica strains showed resistance to ampicillin (92%), streptomycin (13%), and sulfamethoxazole (2%). Intermediate susceptibility to tetracycline was shown by two Y. enterocolitica strains. All Y. pseudotuberculosis strains were susceptible to all tested antimicrobial agents. Most (99%) of the Y. enterocolitica strains carried both β-lactamase genes. One strain of bioserotype 3/O:3 lacked both genes. In contrast, all Y. pseudotuberculosis strains carried neither of the β-lactamase genes. Homogeneity was detected in all blaA and blaB genes of Y. enterocolitica using PCR-RFLP. The majority (89%) of Y. enterocolitica strains expressed both β-lactamase enzymes, whereas none of the Y. pseudotuberculosis strains showed expression of either enzyme. Also, it seems that the resistance of Y. enterocolitica has not changed during the last years.

Shotgun sequencing of Yersinia enterocolitica strain W22703 (biotype 2, serotype O:9): genomic evidence for oscillation between invertebrates and mammals.

BackgroundYersinia enterocolitica strains responsible for mild gastroenteritis in humans are very diverse with respect to their metabolic and virulence properties. Strain W22703 (biotype 2, serotype O:9) was recently identified to possess nematocidal and insecticidal activity. To better understand the relationship between pathogenicity towards insects and humans, we compared the W22703 genome with that of the highly pathogenic strain 8081 (biotype1B; serotype O:8), the only Y. enterocolitica strain sequenced so far.ResultsWe used whole-genome shotgun data to assemble, annotate and analyse the sequence of strain W22703. Numerous factors assumed to contribute to enteric survival and pathogenesis, among them osmoregulated periplasmic glucan, hydrogenases, cobalamin-dependent pathways, iron uptake systems and the Yersinia genome island 1 (YGI-1) involved in tight adherence were identified to be common to the 8081 and W22703 genomes. However, sets of ~550 genes revealed to be specific for each of them in comparison to the other strain. The plasticity zone (PZ) of 142 kb in the W22703 genome carries an ancient flagellar cluster Flg-2 of ~40 kb, but it lacks the pathogenicity island YAPIYe, the secretion system ysa and yts1, and other virulence determinants of the 8081 PZ. Its composition underlines the prominent variability of this genome region and demonstrates its contribution to the higher pathogenicity of biotype 1B strains with respect to W22703. A novel type three secretion system of mosaic structure was found in the genome of W22703 that is absent in the sequenced strains of the human pathogenic Yersinia species, but conserved in the genomes of the apathogenic species. We identified several regions of differences in W22703 that mainly code for transporters, regulators, metabolic pathways, and defence factors.ConclusionThe W22703 sequence analysis revealed a genome composition distinct from other pathogenic Yersinia enterocolitica strains, thus contributing novel data to the Y. enterocolitica pan-genome. This study also sheds further light on the strategies of this pathogen to cope with its environments.

Flagellin genes of Yersinia enterocolitica biotype 1A: playground of evolution towards novel flagellin functions

Yersinia enterocolitica strain 8081, representing the high-pathogenic biotype 1B, harbours three flagellin genes arranged in tandem in the order fliC3, fliC, fliC2. The genes are organized monocistronic but coordinately expressed under the control of the flagellar sigma factor. No sequence data is available on flagellins of low-pathogenic Y. enterocolitica biotypes 2-5 and of biotype 1A strains, appearing non-pathogenic in the mouse infection model. We sequenced the flagellin genes of ten biotype 1A and biotype 4 isolates, respectively. While we could not identify any sequence polymorphism among flagellin genes of biotype 4 isolates, we found that biotype 1A strains harbour three variable flagellin genes. Moreover, three biotype 1A isolates exhibited a rearranged flagellin gene order and at least one rearranged flagellin gene was apparently acquired by horizontal gene transfer. The variability of flagellin genes seems to mirror evolution towards novel flagellin functions. By contrast, strictly conserved flagellins of biotype 4 isolates point at a strong selection pressure such as expected to be imposed by an important function in the context of infection.

The sequence of the pYV virulence plasmid from Yersinia enterocolitica strain WA-314 biogroup 1B serotype O:8

Our laboratory strain Yersinia enterocolitica strain WA-314 biogroup 1B serotype O:8 displayed a different adhesion behavior to host cells compared to other Yersinia strains. To investigate whether this is based on differences in the gene content of the large pYV virulence plasmid which contains the major Yersinia adhesin YadA, we set out to sequence pYV WA-314. pYV WA-314 is very similar to pYV127/90, with a notable difference in the length of the Type III secretion system component YscP, which determines the needle length of the system. We found that we could improve the annotation of proteins previously described as “hypothetical” in pYV127/90 and other pYV plasmids, and show that pYV plasmids contain several and seemingly redundant plasmid partitioning and stabilization systems, explaining why these plasmids are not easily lost in laboratory cultures of Yersinia strains.

Fluoroquinolone and multidrug resistance phenotypes associated with the overexpression of AcrAB and an orthologue of MarA in Yersinia enterocolitica

Quinolone resistance among clinical isolates is of increasing importance. This phenotype particularly affects the nalidixic acid resistance levels and is also increasing among Yersinia enterocolitica strains. This study investigated the quinolone resistance mechanisms acquired in vitro by a Y. enterocolitica clinical isolate exposed to increasing concentrations of ciprofloxacin in a multi-step selection process. The fluoroquinolone-susceptible clinical isolate, Y.83-wt, the fluoroquinolone-resistant mutant, Y.83-64, and intermediate mutants were analysed by QRDR sequencing and MIC determination. Four different QRDRs (quinolone resistance-determining regions) mutations were characterised in Y.83-64: one in gyrA, one in gyrB, and two in parC. A significant increase in the MICs of ciprofloxacin, norfloxacin, nalidixic acid, and other unrelated antibiotics was detected in Y.83-64. Furthermore, the bacterial growth rate was assessed for strains Y.83-wt and Y.83-64. The analysis reported no significant differences between both strains. Cell envelope protein approach revealed an overexpression of both AcrA and AcrB proteins in Y.83-64. RT-PCR analyses were also carried out as was sequencing of known AcrAB regulators in Yersinia. The RT-PCR analysis showed an increased transcriptional level of a marA orthologue, marA Ye , in Y.83-64. The sequencing results reported no change in the acrR gene or in the promoter sequence of the acrAB operon when comparing Y.83-wt with Y.83-64. One differential mutation was detected within the marA Ye promoter in Y.83-64. Thus, the fluoroquinolone resistance phenotype acquired by Y.83-64 relies on the acquisition of 4 QRDR mutations in addition to the overexpression of AcrAB, which is likely triggered by increased expression levels of marA Ye .

Pathogenic Strains ofYersinia enterocoliticaIsolated from Domestic Dogs (Canis familiaris) Belonging to Farmers Are of the Same Subtype as PathogenicY. enterocoliticaStrains Isolated from Humans and May Be a Source of Human Infection in Jiangsu Province, China

We isolated 326 Yersinia enterocolitica strains from 5,919 specimens from patients with diarrhea at outpatient clinics, livestock, poultry, wild animals, insect vectors, food, and the environment in the cities of Nantong and Xuzhou in Jiangsu Province, China, from 2004 to 2008. The results showed that the 12 pathogenic strains were of the O:3 serotype. Six strains were isolated from domestic dogs (Canis familiaris) belonging to farmers and were found to be the primary carriers of pathogenic Y. enterocolitica strains, especially in Xuzhou. Pulsed-field gel electrophoresis analysis of the pathogenic strains from dogs belonging to farmers showed that they shared the same patterns as strains from diarrhea patients isolated in 1994. This indicates that the strains from domestic dogs have a close correlation with the strains causing human infections.

EFFECTS OF ORGANIC ACIDS, NISIN, LYZOZYME AND EDTA ON THE SURVIVAL OF YERSINIA ENTEROCOLITICA POPULATION IN INOCULATED ORANGE BEVERAGES

ABSTRACT Inactivation of a Yersinia enterocolitica strain by 3.4% ascorbic acid (AA), 0.5% citric acid (CA), 0.2% lactic acid, 100 IU/mL nisin, 2,400 IU/mL lysozyme and 20 mM ethylenediaminetetraacetic acid disodium salt (EDTA ), alone and combined, was studied at different temperatures (4 and 25C) in commercial and laboratory‐prepared orange beverages. In laboratory‐prepared juice, highest reductions (between 3.06 and 4.07 log units) were obtained with acid mixtures at 25C after 20 min of incubation. At 24 h of incubation, EDTA was bactericidal and the mixtures with nisin or lysozyme resulted in count reductions of 6.03 and 5.98 log units, respectively. In commercial orange beverage, AA and CA gave reductions of 5.43 and 4.26 log units, respectively. The three acid mixtures were bactericidal within the first 10 min. EDTA alone or mixed completely inhibited Y. enterocolitica strain at 6 and 24 h of incubation. At 4C, all the results were significantly lower than at 25C.PRACTICAL APPLICATIONS Yersinia enterocolitica is a common cause of gastrointestinal disorders and may lead to sequelae. This pathogen can maintain its virulence in a wide temperature range and under adverse conditions such as pH lower than 4. There are reports describing the isolation of Y. enterocolitica from water and ice in Brazil and Latin America. The sale of unpasteurized drinks is a common practice in our region and their consumption has increased over the past years. In the present work, chemical compounds and biological inhibitors were studied. Some of these compounds showed to be efficient for reducing Y. enterocolitica populations. Furthermore, they did not modify the organoleptic characteristics of the beverages and they are not toxic for human beings.

Diagnostic Bioluminescent Phage for Detection of Yersinia pestis

Yersinia pestis is the etiological agent of the plague. Because of the disease's inherent communicability, rapid clinical course, and high mortality, it is critical that an outbreak, whether it is natural or deliberate, be detected and diagnosed quickly. The objective of this research was to generate a recombinant luxAB ("light")-tagged reporter phage that can detect Y. pestis by rapidly and specifically conferring a bioluminescent signal response to these cells. The bacterial luxAB reporter genes were integrated into a noncoding region of the CDC plague-diagnostic phage phiA1122 by homologous recombination. The identity and fitness of the recombinant phage were assessed through PCR analysis and lysis assays and functionally verified by the ability to transduce a bioluminescent signal to recipient cells. The reporter phage conferred a bioluminescent phenotype to Y. pestis within 12 min of infection at 28 degrees C. The signal response time and signal strength were dependent on the number of cells present. A positive signal was obtained from 10(2) cells within 60 min. A signal response was not detectable with Escherichia coli, although a weak signal (100-fold lower than that with Y. pestis) was obtained with 1 (of 10) Yersinia enterocolitica strains and 2 (of 10) Yersinia pseudotuberculosis strains at the restrictive temperature. Importantly, serum did not prevent the ability of the reporter phage to infect Y. pestis, nor did it significantly quench the resulting bioluminescent signal. Collectively, the results indicate that the reporter phage displays promise for the rapid and specific diagnostic detection of cultivated Y. pestis isolates or infected clinical specimens.

Monitoring of plasmid dissociation and pathogenic potential amongYersinia enterocolotica andYersinia pseudotuberculosis during storage of refrigerated pork meat

To determine the pathogenic potential ofYersinia in pork meat samples, different strains ofYersinia enterocolitica andYersinia pseudotuberculosis were inoculated on pieces of raw pork meat samples and exposed to +4 °C and −20 °C for 90 days. The effect of temperature, pH, total bacterial number, and inoculation dose of meat samples on virulence plasmid dissociation among different serotypes ofY. enterocolitica andY. pseudotuberculosis was monitored by using modified cultural media and confirmed by PCR assay andin vivo mouse model. In comparison with the intial dose of contamination,Yersinia cells from the less pathogenic serotypes (O:3 and O:9 ofY. enterocolitica) survived better than the high pathogenic serotypes ofY. enterocolitica O:8 andY. pseudotuberculosis O:3. Maximal rates for plasmid dissociation were found among the cells of the less pathogenic serotypes O:3 and O:9 ofY. enterocolitica. In parallel, at each time point highly virulent phenotypes ofYersinia were proved by direct PCR assay including detection of both chromosomal (ail) and plasmid (virF) genes. The real pathogenic potential ofYersinia cells occurred after plasmid dissociation during long time cold storage was confirmed in a newly designed mouse model mimicking the immunosupression status of humans. Therefore, the impact of refrigeration temperatures differs for theYersinia serotypes and modulates their pathogenic potential resulting in a risk factor for human health.

Prevalence of Yersinia enterocolitica in Market Weight Hogs in the United States

Pigs are the major animal reservoir for Yersinia enterocolitica strains, which are potentially pathogenic for humans. The goals of this study were (i) to estimate the individual animal and on-farm prevalences of Y. enterocolitica in hogs based on tonsil samples collected during National Animal Health Monitoring System Swine 2002 study and (ii) to use these data with data previously published for fecal samples to determine on-farm risk factors for Y. enterocolitica. Tonsil swabs (1,218) and fecal samples (2,847) were collected on 124 farms located in the top 17 pork-producing states. Ten percent of tonsils (122 of 1,218 samples) were positive in irgasan-tiracillin-chlorate (ITC) enrichment broth by real-time PCR, but only 5.6% of samples (68 of 1,218) were positive after subculture on the more selective cefsulodin-irgasan-novobiocin (CIN) agar. For tonsils, the on-farm prevalence based on real-time PCR detection of the ail gene in ITC enrichment broth cultures was 32% (32 of 100 premises sampled); the prevalence based on subculture in CIN agar was 19.6% (20 of 102 premises). Results of bacteriological isolation and real-time PCR analysis of tonsils and feces were combined to estimate prevalence (individual animal and farm), which was subsequently correlated with 40 farm management practices. Four factors and their accompanying odds ratios (ORs) were identified in the final regression model: location in a central state (OR =0.3), vaccination for Escherichia coli (OR = 3.0), percentage of deaths due to scours (OR = 3.5), and presence of meat or bone meal in grower-finisher diet (OR = 4.1).

O:8 serotype Yersinia enterocolitica strains in China

Serotypes O:3, O:8 and O:9 Yersinia enterocolitica strains carrying virulence determinants are common pathogens causing human infections. In many years of surveillance in China for Y. enterocolitica, no pathogenic O:8 strains have been found where the isolated O:8 serotypes lacked the major virulence genes and in contrast to O:3 and O:9 strains, none of the O:8 isolates were from humans. These O:8 isolates lack ail, ystA, yadA and virF genes but possess the ystB gene and all belong to Biotype 1A. These O:8 strains did not kill mice and could protect immunized mice against challenge with a pathogenic O:8 strain. Compared to the Chinese pathogenic O:3 and O:9 strains which have similar pulsed-field gel electrophoresis patterns, the 39 Chinese O:8 animal and food isolates were different from the pathogenic O:8 reference strains. This suggests the O:8 strains lacking virulence determinants may not disseminate rapidly in humans and are maintained in animal reservoirs; and therefore exhibit higher variance and divergence from the virulent type.