Biovar 1A Research Articles

Distribution of virulence-associated genes inYersinia enterocoliticabiovar 1A correlates with clonal groups and not the source of isolation

Yersinia enterocolitica, an important food- and water-borne enteric pathogen, is represented by six biovars viz. 1A, 1B and 2-5. Some biovar 1A strains, despite lacking virulence plasmid (pYV) and chromosomal virulence genes, have been reported to cause symptoms similar to that produced by isolates belonging to known pathogenic biovars. Virulence-associated genes viz. ail, virF, inv, myfA, ystA, ystB, ystC, tccC, hreP, fepA, fepD, fes, ymoA and sat were studied in 81 clinical and nonclinical strains of Y. enterocolitica biovar 1A by PCR amplification. All strains lacked ail, virF, ystA and ystC genes. The distribution of other genes with respect to clonal groups revealed that four genes viz. ystB, hreP, myfA and sat were associated exclusively with strains belonging to clonal group A. The clonal groups A and B were differentiated previously based on rep (REP-/ERIC) - PCR genomic fingerprinting. The distribution of virulence-associated genes, however, did not differ significantly between clinical and nonclinical strains. In strains of Y. enterocolitica biovar 1A, clonal groups seem to reflect virulence potential better than the source (clinical vs. nonclinical) of isolation.

Prevalence of Yersinia enterocolitica in Goat Herds from Northern Germany

The prevalence of human pathogenic Yersinia enterocolitica isolates in livestock farming is of paramount interest. Raw goat milk has been proposed as a source of human yersiniosis; however, no data on the prevalence of human strains of Y. enterocolitica in goat herds are available. Therefore, fecal samples (n = 575) were collected from 24 goat herds from Lower Saxony, northern Germany. Pre-enrichment in peptone, sorbitol and bile salts broth was followed by plating on cefsuloidin irgasan novobiocin agar. Yersinia enterocolitica was isolated from 17 (3%) samples of five (21%) goat herds. All isolates were biovar 1A, but represented various serovars. PCR assays targeting Yersinia adhesin (yad) gene and the yopT gene, both associated with pathogenicity, produced no amplification products. Therefore, the isolates can be regarded as opportunistic apathogenic bacteria. Consequently, milk, cheese or meat from goats should not be considered as an important source for human yersiniosis.

Molecular characterization of β-lactamase genesblaAandblaBofYersinia enterocoliticabiovar 1A

The beta-lactamase genes blaA and blaB were detected by PCR amplification in strains of Yersinia enterocolitica biovar 1A isolated from India, Germany, France and the USA. Both genes were detected in all strains. Polymerase chain reaction-restriction fragment length polymorphism revealed genetic heterogeneity in blaA but not in blaB. Cluster analysis of blaA restriction profiles grouped the strains into three groups. The blaA gene of Y. enterocolitica biovar 1A showed a high degree of sequence homology to that of Y. enterocolitica 8081 (biovar 1B) and Y. enterocolitica Y-56 (biovar 4), whereas homology was low with class A beta-lactamase genes of other members of the family Enterobacteriaceae. The pI 8.7 of enzyme Bla-A of Y. enterocolitica biovar 1A was similar to that of biovars 2, 3 and 4. The enzyme Bla-B focused at 6.8 and 7.1, indicating that biovar 1A strains produced a 'B-like' enzyme. This is the first study to have investigated the genetic heterogeneity of the beta-lactamase genes of Y. enterocolitica.

Low temperature‐induced insecticidal activity of Yersinia enterocolitica

The insecticidal toxin complexes (Tcs) are produced by several Enterobacteriaceae associated with insects, such as Photorhabdus luminescens, Serratia entomophila and Xenorhabdus nematophilus. Genome sequences revealed tc-like genes in Yersinia spp., but insecticidal activity of this genus associated with the toxins has not been described. Through the search for genes upregulated at low growth temperatures in Yersinia enterocolitica strain W22703, a genomic island of 19 kb termed tc-PAI(Ye) with homologues of the toxin genes tcaA, tcaB, tcaC and tccC was identified. Southern blot and polymerase chain reaction (PCR) analysis of 34 strains demonstrated that the tc-PAI(Ye) is present in biovars 2, 3 and 4, but neither in biovars 1A and 1B, nor in five Yersinia species apathogenic in humans. Using the luxCDABE operon as reporter, the expression of the toxin genes was shown to be completely repressed in cells cultured at 37 degrees C, and to increase by 4.6 orders of magnitude when the growth temperature was decreased gradually to 10 degrees C. These data provide the first indication that temperature is a critical parameter for induction or repression of tc gene transcription. Whole-cell extracts of Y. enterocolitica strain W22703 cultivated at 10 degrees C, but not at 30 degrees C, led to insect mortality when fed to Manduca sexta larvae, in contrast to an insertional tcaA mutant. Overall the results suggest that the tc-PAI(Ye) could play an important role in the transmission and survival of pathogenic Y. enterocolitica strains outside mammalian hosts.

Detection and assay of beta-lactamases in clinical and non-clinical strains of Yersinia enterocolitica biovar 1A.

To detect beta-lactamases (A & B) and extended-spectrum beta-lactamases (ESBLs) in clinical and non-clinical isolates of Yersinia enterocolitica biovar 1A, and to determine their activity in the presence of specific lactamase inhibitors. The presence of beta-lactamases and ESBLs was detected by disc diffusion in 219 (36 clinical, 183 non-clinical) isolates. beta-Lactamase activity was assayed spectrophotometrically in all 36 clinical and 10 representative non-clinical isolates using nitrocefin as the substrate. Inhibition of beta-lactamases was studied by clavulanic acid, aztreonam and cloxacillin. Of the 219 isolates, all except two non-clinical isolates indicated the presence of beta-lactamase A (Bla-A) based on the smaller (2-8 mm) radius of the inhibition zone around the ticarcillin disc. Synergy between ticarcillin and co-amoxiclav discs was, however, observed in only 34% of isolates of non-clinical origin. beta-Lactamase B (Bla-B) was found to be consistently positive among all the clinical and non-clinical isolates, as indicated by its characteristic appearance of flattening of the zone of inhibition around the cefotaxime disc adjacent to an imipenem disc. Bla-B was induced more strongly in clinical than in non-clinical isolates. Inhibition of enzyme A by clavulanic acid, aztreonam and cloxacillin was found to be similar, whereas enzyme B was inhibited more strongly by aztreonam and cloxacillin. None of the isolates showed the unequivocal presence of ESBL. This is the first report on beta-lactamases of Yersinia enterocolitica biovar 1A from Asia. Y. enterocolitica biovar 1A expressed both Bla-A and Bla-B. Heterogeneity was, however, discerned in the expression of Bla-A and by induction of Bla-B among clinical and non-clinical isolates of Y. enterocolitica biovar 1A.

Beta-lactamase expression in Yersinia enterocolitica biovars 1A, 1B, and 3.

Characteristic patterns of beta-lactam susceptibility are associated with different biovars of Yersinia enterocolitica. In a previous study differences in beta-lactam susceptibility among biovar 2, 4 and 5 strains were largely attributed to differences in expression of beta-lactamase A (BlaA) and beta-lactamase B (BlaB). The basis for differences in beta-lactam susceptibility of strains of biovars 1A, 1B and 3 is now considered. All the strains examined had blaB; nine of 31 biovar 3 strains and two of 13 biovar 1B strains had blaA, but PCR did not amplify blaA from biovar 1A strains. Nevertheless, inhibition data indicated that the majority of uninduced biovar 1A strains expressed BlaA and BlaB in similar amounts. Strong inducibility was seen in all these strains. Biovar 1B strains (which were less inducible than strains of biovar 1A) predominantly produced BlaA without induction; ticarcillin-sensitive strains of biovar 3 produced only BlaB but were not inducible; without induction biovar 3 strains resistant to ticarcillin and amoxycillin/clavulanate produced either predominantly BlaA, predominantly BlaB or exclusively BlaB and induction was demonstrated except for strains producing BlaB alone; biovar 3 strains resistant to ticarcillin but sensitive to amoxycillin/clavulanate predominantly produced BlaA without induction and were inducible for beta-lactamase activity. After induction, nearly all strains predominantly or exclusively produced BlaB. Although PCR amplification fragments with primers specific for blaA were obtained only from some strains, the induction and inhibition data suggest that all Y. enterocolitica strains possess enzymes related to BlaA- as well as BlaB. Nevertheless, expression of the beta-lactamase is regulated differently in different biovars and varies within most biovars. Failure to predict beta-lactamase expression profiles from MIC data indicates the presence of additional mechanisms contributing to differences in susceptibility.

An in-vitro study of the antimicrobial susceptibilities of Yersinia enterocolitica and the definition of a database.

The antibiotic susceptibilities of 151 Yersinia enterocolitica strains isolated from humans, animals and the environment, and belonging to biovars 1A (n = 22), 1B (n = 13), 2 (n = 12), 3 (n = 31), 4 (n = 63) and 5 (n = 10) to 71 antibiotics were examined. Biovars could be characterized phenotypically by their similar antibiograms. For the majority of biovars only minor differences in susceptibilities were detected. Ninety-nine percent of all Yersinia strains were resistant to amoxycillin, but biovar-related differences in MICs were demonstrated. Significant differences, characteristic of specific biovars, were detected for fosfomycin, some beta-lactams (in particular amoxycillin/clavulanate, and ticarcillin). Strains of biovar 1A were resistant or of intermediate susceptibility to ticarcillin and had fosfomycin MICs of 16-64 mg/L and amoxycillin/clavulanate MICs of 4-32 mg/L. Most strains of biovar 1B (n = 11) were sensitive to amoxycillin/clavulanate (MIC = 0.5-2 mg/L). Most strains of biovar 2 (n = 10) showed an antibiotic phenotype resembling that of strains of biovar 1A, but they were more susceptible to fosfomycin (MIC = 4-16 mg/L). Twenty-seven strains of biovar 3 had amoxycillin/clavulanate MICs of 4-32 mg/L; 19 of them were sensitive to ticarcillin and fosfomycin. Biovar 4 strains were uniformly sensitive or of intermediate susceptibility to amoxycillin/clavulanate (MIC = 0.5-4 mg/L), sensitive to fosfomycin (MIC = 1-4 mg/L) but resistant to ticarcillin. The prevailing antibiotic phenotype of biovar 5 (n = 7) was similiar to the phenotype of biovar 4, although these biovar 5 strains were slightly more susceptible to amoxycillin/clavulanate and showed a heterogeneous pattern of susceptibility to fosfomycin (MIC = 1-32 mg/L). The results of this study show that unambiguous statements cannot be made about the natural antibiotic susceptibility to certain beta-lactams and fosfomycin of Y. enterocolitica. The data indicate a complex regulation of beta-lactamases in Y. enterocolitica. Some beta-lactamases are found more frequently or will be expressed predominantly in specific biovars.

Is natural genetic transformation a mechanism of horizontal gene transfer in Yersinia?

We investigated the capacity of different Yersinia strains with emphasis to Yersinia enterocolitica to take up and incorporate DNA by natural genetic transformation. Our studies were initiated by the observation of partial homology between the virulence plasmid of a pathogenic Y. enterocolitica strain (O: 3, biovar 4) and plasmids indiginous to different a pathogenic Y. enterocolitica biovar 1A strains revealed by hybridization studies. Furthermore, an observation of natural genetic transformation in a strain of Y. enterocolitica has been published by CALLAHAN and KOROMA (1979). To detect an uptake and incorporation of DNA, we incubated potential recipient strains with naked DNA under varying experimental conditions. The parameters tested were--the recipient strain,--the markers used to detect a DNA transfer,--the condition of the transforming DNA,--the nutrient availability,--the temperature,--the growth phase, and--the influence of stress. In our experiments, we could not identify conditions under which Y. enterocolitica could be naturally transformed. We thus conclude that natural transformation is unlikely to be an important mechanism for horizontal gene transfer in Yersinia.

Comparison of Plasmids of Strains of Yersinia enterocolitica Biovar 1A with the virulence Plasmid of a Pathogenic Y. enterocolitica Strain

The plasmid content of apathogenic Y. enterocolitica biovar 1A strains was determined and the plasmids were compared with the virulence plasmid of a pathogenic Y. enterocolitica strain. About 38% of the selected biovar 1A strains contained plasmids of different sizes ranging from 2.7 kb to more than 70 kb. Some of the larger plasmids had a size similar to that of the virulence plasmid of a pathogenic reference strain. The restriction patterns of these plasmids were different from the restriction pattern of the virulence plasmid of the pathogenic reference strain. Differences were also observed in hybridization studies with the virulence plasmid. The plasmids from 15 out of 16 biovar 1A strains showed no homology, whereas the plasmid of one biovar 1A strain partially hybridized to the virulence plasmid.