PCR detection of virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis and investigation of virulence gene distribution

PCR-based assays were developed for the detection of plasmid- and chromosome-borne virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis, to investigate the distribution of these genes in isolates from various sources. The results of PCR genotyping, based on 5 virulence-associated genes of 140 strains of Y. enterocolitica, were compared to phenotypic tests, such as biotyping and serotyping, and to virulence plasmid-associated properties such as calcium-dependent growth at 37 degrees C and Congo red uptake. The specificity of the PCR results was validated by hybridization. Genotyping data correlated well with biotype data, and most biotypes resulted in (nearly) homogeneous genotypes for the chromosomal virulence genes (ystA, ystB, and ail); however, plasmid-borne genes (yadA and virF) were detected with variable efficiency, due to heterogeneity within the bacterial population for the presence of the virulence plasmid. Of the virulence genes, only ystB was present in biotype 1A; however, within this biotype, pathogenic and apathogenic isolates could not be distinguished based on the detection of virulence genes. Forty Y. pseudotuberculosis isolates were tested by PCR for the presence of inv, yadA, and lcrF. All isolates were inv positive, and 88% of the isolates contained the virulence plasmid genes yadA and lcrF. In conclusion, this study shows that genotyping of Yersinia spp., based on both chromosome- and plasmid-borne virulence genes, is feasible and informative and can provide a rapid and reliable genotypic characterization of field isolates.     

Yersinia enterocolitica Isolates from Wild Boars Hunted in Lower Saxony,Germany

Yersiniosis is strongly associated with the consumption of pork contaminated with enteropathogenic Yersinia enterocolitica, which is harbored by domestic pigs without showing clinical signs of disease. In contrast to data on Y. enterocolitica isolated from conventionally reared swine, investigations into the occurrence of Y. enterocolitica in wild boars in Germany are rare. The objectives of the study were to get knowledge about these bacteria and their occurrence in wild boars hunted in northern Germany by isolation of the bacteria from the tonsils, identification of the bioserotypes, determination of selected virulence factors, macrorestriction analysis, multilocus sequence typing (MLST), and testing of antimicrobial susceptibility. Altogether, tonsils from 17.1% of 111 tested wild boars were positive for Y. enterocolitica by culture methods. All but two isolates belonged to biotype (BT) 1A, with the majority of isolates bearing a ystB nucleotide sequence which was revealed to have 85% identity to internal regions of Y. enterocolitica heat-stable enterotoxin type B genes. The remaining Y. enterocolitica isolates were identified to be BT 1B and did not carry the virulence plasmid. However, two BT 1A isolates carried the ail gene. Macrorestriction analysis and results from MLST showed a high degree of genetic diversity of the isolates, although the region where the samples were taken was restricted to Lower Saxony, Germany, and wild boars were shot during one hunting season. In conclusion, most Y. enterocolitica isolates from wild boars investigated in this study belonged to biotype 1A. Enteropathogenic Y. enterocolitica bioserotypes 4/O:3 and 2/O:9, usually harbored by commercially raised pigs in Europe, could not be identified.     

Structural Organization of Virulence-Associated Plasmids of Yersinia pestis

The complete nucleotide sequence and gene organization of the three virulence plasmids from Yersinia pestis KIM5 were determined. Plasmid pPCP1 (9,610 bp) has a GC content of 45.3% and encodes two previously known virulence factors, an associated protein, and a single copy of IS100. Plasmid pCD1 (70,504 bp) has a GC content of 44.8%. It is known to encode a number of essential virulence determinants, regulatory functions, and a multiprotein secretory system comprising the low-calcium response stimulation that is shared with the other two Yersinia species pathogenic for humans (Y. pseudotuberculosis and Y. enterocolitica). A new pseudogene, which occurs as an intact gene in the Y. enterocolitica and Y. pseudotuberculosis-derived analogues, was found in pCD1. It corresponds to that encoding the lipoprotein YlpA. Several intact and partial insertion sequences and/or transposons were also found in pCD1, as well as six putative structural genes with high homology to proteins of unknown function in other yersiniae. The sequences of the genes involved in the replication of pCD1 are highly homologous to those of the cognate plasmids in Y. pseudotuberculosis and Y. enterocolitica, but their localization within the plasmid differs markedly from those of the latter. Plasmid pMT1 (100,984 bp) has a GC content of 50.2%. It possesses two copies of IS100, which are located 25 kb apart and in opposite orientations. Adjacent to one of these IS100 inserts is a partial copy of IS285. A single copy of an IS200-like element (recently named IS1541) was also located in pMT1. In addition to 5 previously described genes, such as murine toxin, capsule antigen, capsule anchoring protein, etc., 30 homologues to genes of several bacterial species were found in this plasmid, and another 44 open reading frames without homology to any known or hypothetical protein in the databases were predicted.     

Characterization of a Yersinia enterocolitica biotype 1A strain harbouring an ail gene

Aims: The chromosomal ail gene (attachment and invasion locus) is commonly used as target gene for the detection of pathogenic Y. enterocolitica strains in food testing. The ail PCR does not detect strains of biotype 1A (BT1A), which are regarded as non‐pathogenic because BT1A strains lack the virulence plasmid and chromosomally encoded virulence genes. In some recent reports, however, BT1A strains were discovered that harboured the ail gene. We isolated an ail‐positive strain and characterized this strain with phenotypic and genotypic methods to study its possible relation to pathogenic Y. enterocolitica strains. Methods and Results: The ail region of the BT1A strain was sequenced and compared with the corresponding region of nonpathogenic BT1A strains and pathogenic strains. Pulsed field gel electrophoresis (PFGE) analysis was applied revealing no similarity of the PFGE pattern of this strain to the patterns of pathogenic strains. Virulence‐gene‐based PCR analyses showed the strain to be positive for ystB, but negative for virulence genes ystA, virF and yadA. Whole‐cell MALDI‐TOF MS combined with a shrinkage discriminant analysis approach was applied and clearly classified the ail‐positive biotype 1A strain within the cluster of BT1A strains. Conclusions: PCR detection of ail sequences in food matrices should be followed by the isolation of the responsible strain and its characterization using phenotypic or genotypic methods. Significance and Impact of the Study: The ail gene may be present in Y. enterocolitica BT1A strains, which are commonly considered as nonpathogenic. Efficient methods such as PCR typing of other virulence genes or rapid MALDI‐TOF MS‐based bacterial profiling allow a more comprehensive assessment of the pathogenicity potential of Yersinia strains.     

Gene polymorphism analysis of Yersinia enterocolitica outer membrane protein A and putative outer membrane protein A family protein

Background

Yersinia enterocolitica outer membrane protein A (OmpA) is one of the major outer membrane proteins with high immunogenicity. We performed the polymorphism analysis for the outer membrane protein A and putative outer membrane protein A (p-ompA) family protein gene of 318 Y. enterocolitica strains.

Results

The data showed all the pathogenic strains and biotype 1A strains harboring ystB gene carried both ompA and p-ompA genes; parts of the biotype 1A strains not harboring ystB gene carried either ompA or p-ompA gene. In non-pathogenic strains (biotype 1A), distribution of the two genes and ystB were highly correlated, showing genetic polymorphism. The pathogenic and non-pathogenic, highly and weakly pathogenic strains were divided into different groups based on sequence analysis of two genes. Although the variations of the sequences, the translated proteins and predicted secondary or tertiary structures of OmpA and P-OmpA were similar.

Conclusions

OmpA and p-ompA gene were highly conserved for pathogenic Y. enterocolitica. The distributions of two genes were correlated with ystB for biotype 1A strains. The polymorphism analysis results of the two genes probably due to different bio-serotypes of the strains, and reflected the dissemination of different bio-serotype clones of Y. enterocolitica.     

Rapid 5′ Nuclease (TaqMan) Assay for Detection of Virulent Strains of Yersinia enterocolitica

We have developed a rapid procedure for the detection of virulent Yersinia enterocolitica in ground pork by combining a previously described PCR with fluorescent dye technologies. The detection method, known as the fluorogenic 5′ nuclease assay (TaqMan), produces results by measuring the fluorescence produced during PCR amplification, requiring no post-PCR processing. The specificity of the chromosomal yst gene-based assay was tested with 28 bacterial isolates that included 7 pathogenic and 7 nonpathogenic serotypes of Y. enterocolitica, other species of Yersinia (Y. aldovae, Y. pseudotuberculosis, Y. mollaretti, Y. intermedia, Y. bercovieri, Y. ruckeri, Y. frederiksenii, and Y. kristensenii), and other enteric bacteria (Escherichia, Salmonella, Citrobacter, and Flavobacterium). The assay was 100% specific in identifying the pathogenic strains of Y. enterocolitica. The sensitivity of the assay was found to be ≥10² CFU/ml in pure cultures and ≥10³ CFU/g in spiked ground pork samples. Results of the assay with food enrichments prespiked with Y. enterocolitica serotypes O:3 and O:9 were comparable to standard culture results. Of the 100 field samples (ground pork) tested, 35 were positive for virulent Y. enterocolitica with both 5′ nuclease assay and conventional virulence tests. After overnight enrichment the entire assay, including DNA extraction, amplification, and detection, could be completed within 5 h.     

Oligomeric coiled-coil adhesin YadA is a double-edged sword

Yersinia adhesin A (YadA) is an essential virulence factor for the food-borne pathogens Yersinia enterocolitica and Yersinia pseudotuberculosis. Suprisingly, it is a pseudogene in Yersinia pestis. Even more intriguing, the introduction of a functional yadA gene in Y. pestis EV76 was shown to correlate with a decrease in virulence in a mouse model. Here, we report that wild type (wt) Y. enterocolitica E40, as well as YadA-deprived E40 induced the synthesis of neutrophil extracellular traps (NETs) upon contact with neutrophils, but only YadA-expressing Y. enterocolitica adhered to NETs and were killed. As binding seemed to be a prerequisite for killing, we searched for YadA-binding substrates and detected the presence of collagen within NETs. E40 bacteria expressing V98D,N99A mutant YadA with a severely reduced ability to bind collagen were found to be more resistant to killing, suggesting that collagen binding contributes significantly to sensitivity to NETs. Wt Y. pestis EV76 were resistant to killing by NETs, while recombinant EV76 expressing YadA from either Y. pseudotuberculosis or Y. enterocolitica were sensitive to killing by NETs, outlining the importance of YadA for susceptibility to NET-dependent killing. Recombinant EV76 endowed with YadA from Y. enterocolitica were also less virulent for the mouse than wt EV76, as shown before. In addition, EV76 carrying wt YadA were less virulent for the mouse than EV76 expressing YadA_V98D,N99A. The observation that YadA makes Yersinia sensitive to NETs provides an explanation as for why evolution selected for the inactivation of yadA in the flea-borne Y. pestis and clarifies an old enigma. Since YadA imposes the same cost to the food-borne Yersinia but was nevertheless conserved by evolution, this observation also illustrates the duality of some virulence functions.     

Genotyping of Human and Porcine Yersinia enterocolitica, Yersinia intermedia, and Yersinia bercovieri Strains from Switzerland by Amplified Fragment Length Polymorphism Analysis

In this study, 231 strains of Yersinia enterocolitica, 25 strains of Y. intermedia, and 10 strains of Y. bercovieri from human and porcine sources (including reference strains) were analyzed using amplified fragment length polymorphism (AFLP), a whole-genome fingerprinting method for subtyping bacterial isolates. AFLP typing distinguished the different Yersinia species examined. Representatives of Y. enterocolitica biotypes 1A, 1B, 2, 3, and 4 belonged to biotype-related AFLP clusters and were clearly distinguished from each other. Y. enterocolitica biotypes 2, 3, and 4 appeared to be more closely related to each other (83% similarity) than to biotypes 1A (11%) and 1B (47%). Biotype 1A strains exhibited the greatest genetic heterogeneity of the biotypes studied. The biotype 1A genotypes were distributed among four major clusters, each containing strains from both human and porcine sources, confirming the zoonotic potential of this organism. The AFLP technique is a valuable genotypic method for identification and typing of Y. enterocolitica and other Yersinia spp.     

Yersinia enterocolitica Infection and tcaA-Dependent Killing of Caenorhabditis elegans

Caenorhabditis elegans is a validated model to study bacterial pathogenicity. We report that Yersinia enterocolitica strains {"type":"entrez-nucleotide","attrs":{"text":"W22703","term_id":"1299536","term_text":"W22703"}}W22703 (biovar 2, serovar O:9) and WA314 (biovar 1B, serovar O:8) kill C. elegans when feeding on the pathogens for at least 15 min before transfer to the feeding strain Escherichia coli OP50. The killing by Yersinia enterocolitica requires viable bacteria and, in contrast to that by Yersinia pestis and Yersinia pseudotuberculosis strains, is biofilm independent. The deletion of tcaA encoding an insecticidal toxin resulted in an OP50-like life span of C. elegans, indicating an essential role of TcaA in the nematocidal activity of Y. enterocolitica. TcaA alone is not sufficient for nematocidal activity because E. coli DH5α overexpressing TcaA did not result in a reduced C. elegans life span. Spatial-temporal analysis of C. elegans infected with green fluorescent protein-labeled Y. enterocolitica strains showed that Y. enterocolitica colonizes the nematode intestine, leading to an extreme expansion of the intestinal lumen. By low-dose infection with {"type":"entrez-nucleotide","attrs":{"text":"W22703","term_id":"1299536","term_text":"W22703"}}W22703 or DH5α followed by transfer to E. coli OP50, proliferation of Y. enterocolitica, but not E. coli, in the intestinal lumen of the nematode was observed. The titer of {"type":"entrez-nucleotide","attrs":{"text":"W22703","term_id":"1299536","term_text":"W22703"}}W22703 cells within the worm increased to over 10⁶ per worm 4 days after infection while a significantly lower number of a tcaA knockout mutant was recovered. A strong expression of tcaA was observed during the first 5 days of infection. Y. enterocolitica WA314 (biovar 1B, serovar O:8) mutant strains lacking the yadA, inv, yopE, and irp1 genes known to be important for virulence in mammals were not attenuated or only slightly attenuated in their toxicity toward the nematode, suggesting that these factors do not play a significant role in the colonization and persistence of this pathogen in nematodes. In summary, this study supports the hypothesis that C. elegans is a natural host and nutrient source of Y. enterocolitica.Yersinia enterocolitica belongs to the family of Enterobacteriaceae and is a psychrotolerant human pathogen that causes gastrointestinal syndromes ranging from acute enteritis to mesenteric lymphadenitis (5). It infects a number of mammals, and swine was identified as a major source for human infection (6). A multiphasic life cycle, which comprises a free-living phase and several host-associated phases, including cold-blooded and warm-blooded hosts, appears to be characteristic for biovars 1B and 2 to 5 of Y. enterocolitica (7, 24).Nonmammalian host organisms including Dictyostelium discoideum, Drosophila melanogaster, or Caenorhabditis elegans are increasingly used to study host-pathogen interactions (16, 26). Due to the obvious parallels between the mammalian and invertebrate defense mechanisms, it has been suggested that the bacteria-invertebrate interaction has shaped the evolution of microbial pathogenicity (53). Several human pathogens including Gram-positive and Gram-negative bacteria infect and kill the soil nematode C. elegans when they are supplied as a nutrient source (42). For example, Streptococcus pneumoniae (4), Listeria monocytogenes (50), extraintestinal Escherichia coli (15), and Staphylococcus aureus (43) but not Bacillus subtilis have been shown to kill the nematode. Upon infection of C. elegans with Enterococcus faecalis, Gram-positive virulence-related factors as well as putative antimicrobials have been identified (20, 35). The extensive conservation in virulence mechanisms directed against invertebrates as well as mammals was demonstrated using a screen with Pseudomonas aeruginosa (30). In this study, 10 of 13 genes whose knockout attenuated the nematode killing were also required for full virulence in a mouse model, confirming the suitability of the C. elegans model to study bacterial pathogenicity. C. elegans is also colonized by Salmonella enterica serovar Typhimurium (S. Typhimurium). This process requires Salmonella virulence factors and was used to study the innate immune response of the nematode (1, 2, 49).The effect of pathogenic Yersinia spp. on C. elegans has also been investigated. It could be demonstrated that both Yersinia pestis and Yersinia pseudotuberculosis block food intake by creating a biofilm around the worm''s mouth (13, 27). This biofilm formation requires the hemin storage locus (hms) and has been suggested to be responsible for the blockage of the digestive tract following uptake by fleas, thus acting as a bacterial defense against predation by invertebrates. In a study with 40 Y. pseudotuberculosis strains, one-quarter of them caused an infection of C. elegans by biofilm formation on the worm head (27). In contrast, a similar effect was not observed following nematode infection with 15 Y. enterocolitica strains. Using a Y. pestis strain lacking the hms genes, it could be demonstrated that this mutant can infect and kill the nematode by a biofilm-independent mechanism that includes the accumulation of Y. pestis in the intestine of the worm (47). This pathogenesis model was applied to show that putative virulence factors such as YapH, OmpT, or a metalloprotease, Y3857, but not the virulence plasmids pCD1 and pPCP1, are required for Y. pestis virulence in C. elegans. Six yet unknown genes required for full virulence in C. elegans were also identified, and one of them appeared to be a virulence factor in the mouse infection model.C. elegans has not been used to study the pathogenicity properties of Y. enterocolitica, mainly due to the fact that many of its virulence factors are upregulated at 37°C in comparison to growth at lower temperatures while C. elegans cannot be cultivated at temperatures above 25°C. In this study, we examined for the first time the infection of C. elegans by Y. enterocolitica strains, demonstrating that this pathogen colonizes and kills C. elegans and that the insecticidal toxin TcaA, which is expressed only at ambient temperature, is required for full nematocidal activity.     

Evaluation of Virulence Test Procedures for Yersinia enterocolitica Recovered from Foods

Recently a heat stable toxin (ST) and the vw factors of the plague bacteria were identified in Yersinia enterocolitica recovered from human infections. The vw factors were reported to be associated with a plasmid of 42-46 M Daltons in size and were essential for the expression of virulence. With this knowledge virulence tests were developed which allowed us to assess the virulence potential of food-borne Y. enterocolitica regardless of biotypes or serotypes. The tests evaluated were: (1) rapid presumptive test for the virulence plasmid; (2) gel electrophoretic confirmation of the virulence plasmid; (3) Laird's qualitative oral feeding test with thirst stressed mice; (4) quantitative LD₅₀ determination by i.p. injection of the mouse lethal ( i.e. serotype 0:8) strains in saline; (5) quantitative LD₅₀ determination of mouse non-lethal ( i.e. serotype 0:3) strains by i.p. injection of these strains suspended in 1 ml of 10% iron dextran saline solution for virulence enhancement. These tests were evaluated with the serotypes 0:3 and 0:8 strains associated with human infections with and without the virulence plasmid with reproducible results. Then the virulence tests procedures were applied to 79 food isolates. The virulence plasmid was detected only in the Nilehn biotype 2, 3 and 4 strains, but it was absent in Nilehn biotype 1 or the atypical strains that ferment rhamnose. The virulence of food and clinical isolates of Y. enterocolitica can be assayed fairly accurately with the above tests.     

Identification and Characterization of Pathogenic Yersinia enterocolitica Isolates by PCR and Pulsed-Field Gel Electrophoresis

Approximately 550 to 600 yersiniosis patients are reported annually in Sweden. Although pigs are thought to be the main reservoir of food-borne pathogenic Yersinia enterocolitica, the role of pork meat as a vehicle for transmission to humans is still unclear. Pork meat collected from refrigerators and local shops frequented by yersiniosis patients (n = 48) were examined for the presence of pathogenic Yersinia spp. A combined culture and PCR method was used for detection, and a multiplex PCR was developed and evaluated as a tool for efficient identification of pathogenic food and patient isolates. The results obtained with the multiplex PCR were compared to phenotypic test results and confirmed by pulsed-field gel electrophoresis (PFGE). In all, 118 pork products (91 raw and 27 ready-to-eat) were collected. Pathogenic Yersinia spp. were detected by PCR in 10% (9 of 91) of the raw pork samples (loin of pork, fillet of pork, pork chop, ham, and minced meat) but in none of the ready-to-eat products. Isolates of Y. enterocolitica bioserotype 4/O:3 were recovered from six of the PCR-positive raw pork samples; all harbored the virulence plasmid. All isolates were recovered from food collected in shops and, thus, none were from the patients' home. When subjected to PFGE, the six isolates displayed four different NotI profiles. The same four NotI profiles were also present among isolates recovered from the yersiniosis patients. The application of a multiplex PCR was shown to be an efficient tool for identification of pathogenic Y. enterocolitica isolates in naturally contaminated raw pork.     

Application of Fluorescent Amplified Fragment Length Polymorphism for Comparison of Human and Animal Isolates of Yersinia enterocolitica

An amplified fragment length polymorphism (AFLP) method, developed to genotype Yersinia enterocolitica, has been used to investigate 70 representative strains isolated from humans, pigs, sheep, and cattle in the United Kingdom. AFLP primarily distinguished Y. enterocolitica strains according to their biotype, with strains dividing into two distinct clusters: cluster A, comprising largely the putatively pathogenic biotypes (BT2 to -4), and cluster B, comprising the putatively nonpathogenic biotype 1A strains and a single BT1B isolate. Within these two clusters, subclusters formed largely on the basis of serotype. However, AFLP profiles also allowed differentiation of strains within these serotype-related subclusters, indicating the high discriminatory power of the technique for Y. enterocolitica. Investigation of the relationship between strain AFLP profile and host confirmed that pigs are, and provides further proof that sheep may be, potential sources of human infection with putatively pathogenic strains. However, the results suggest that some strains causing human disease do not come from veterinary sources identifiable at this time. The distribution of some BT1A isolates within cluster A raises questions about the relationship between virulence potential and biotype.     

The complete genome sequence and comparative genome analysis of the high pathogenicity Yersinia enterocolitica strain 8081

The human enteropathogen, Yersinia enterocolitica, is a significant link in the range of Yersinia pathologies extending from mild gastroenteritis to bubonic plague. Comparison at the genomic level is a key step in our understanding of the genetic basis for this pathogenicity spectrum. Here we report the genome of Y. enterocolitica strain 8081 (serotype 0:8; biotype 1B) and extensive microarray data relating to the genetic diversity of the Y. enterocolitica species. Our analysis reveals that the genome of Y. enterocolitica strain 8081 is a patchwork of horizontally acquired genetic loci, including a plasticity zone of 199 kb containing an extraordinarily high density of virulence genes. Microarray analysis has provided insights into species-specific Y. enterocolitica gene functions and the intraspecies differences between the high, low, and nonpathogenic Y. enterocolitica biotypes. Through comparative genome sequence analysis we provide new information on the evolution of the Yersinia. We identify numerous loci that represent ancestral clusters of genes potentially important in enteric survival and pathogenesis, which have been lost or are in the process of being lost, in the other sequenced Yersinia lineages. Our analysis also highlights large metabolic operons in Y. enterocolitica that are absent in the related enteropathogen, Yersinia pseudotuberculosis, indicating major differences in niche and nutrients used within the mammalian gut. These include clusters directing, the production of hydrogenases, tetrathionate respiration, cobalamin synthesis, and propanediol utilisation. Along with ancestral gene clusters, the genome of Y. enterocolitica has revealed species-specific and enteropathogen-specific loci. This has provided important insights into the pathology of this bacterium and, more broadly, into the evolution of the genus. Moreover, wider investigations looking at the patterns of gene loss and gain in the Yersinia have highlighted common themes in the genome evolution of other human enteropathogens.     

Biochemical heterogeneity of serotype 03 strains of 700Yersinia strains isolated from humans,other mammals,flies, animal feed,and river water

A total of 700 serotype 03 strains of yersiniae were recovered from patients, households withYersinia enterocolitica-infected persons, healthy humans, pigs, dogs, flies, feed, and river water, from 1977 to 1983. Of these isolates, 695 belonged toYersinia enterocolitica, three toYersinia intermedia, and two toYersinia frederiksenii. The 695Y. enterocolitica strains were classified into 484 biotype 4 serotype 03 phage type VIII, 17 biotype 4A (ornithine decarboxylase-negative) serotype 03 phage type VIII, 15 biotype 4B (maltosenegative) serotype 03 phage type VIII, and 179 biotype 3B (VP-, sorbose-, and inositolnegative) serotype 03 phage type II. These four biochemical heterogeneous types, including three new types, ofY. enterocolitica probably have long existed in Japan. There was a close relation between human infection withY. enterocolitica and the harboring ofY. enterocolitica in pigs and dogs.     

Unique Activity Spectrum of Colicin FY: All 110 Characterized Yersinia enterocolitica Isolates Were Colicin FY Susceptible

Colicin F_Y is a plasmid encoded toxin that recognizes a yersinia-specific outer membrane protein (YiuR) as a receptor molecule. We have previously shown that the activity spectrum of colicin F_Y comprises strains of the genus Yersinia. In this study, we analyzed the activity of colicin F_Y against 110 Yersinia enterocolitica isolates differing in geographical origin and source. All isolates were characterized through analysis of 16S rRNA genes, serotyping, biotyping, restriction profiling of genomic DNA, detection of virulence markers and susceptibility to antibiotics. This confirmed the broad variability of the collection, in which all 110 Y. enterocolitica isolates, representing 77 various strains, were inhibited by colicin F_Y. Although isolates showed variable levels of susceptibility to colicin F_Y, it was not associated with any strain characteristic. The universal susceptibility of Y. enterocolitica strains to colicin F_Y together with the absence of activity towards strains outside the Yersinia genus suggests potential therapeutic applications for colicin F_Y.     

Yersinia pseudotuberculosis in China

Thirty strains of Yersinia pseudotuberculosis were isolated from rabbits (17 strains), wild rats (9 strains) and house rats (4 strains) in China between 1990 and 1993. The biochemical properties of these isolates were identical with those of Y. pseudotuberculosis and no special characteristics were found in these strains. Serologically, serogroups 4b and 5b were identical to isolates found in Japan, and a new serogroup 1c and unclassified strains have also been detected. The existence of virulence-associated properties were different among strains. The pYV plasmid was detected from 6 strains of 30 isolates. This report documents the presence of Y. pseudotuberculosis in China, providing important epidemiological information.