Plasmids and lack of pathogenicity of Yersinia enterocolitica isolated from wild-living birds, Japanese serows and environmental specimens

Generalized transduction of small Yersinia enterocolitica plasmids

To study phage-mediated gene transfer in Yersinia, the ability of Yersinia phages to transduce naturally occurring plasmids was investigated. The transduction experiments were performed with a temperate phage isolated from a pathogenic Yersinia enterocolitica strain and phage mixtures isolated from sewage. Small plasmids (4.3 and 5.8 kb) were transduced at a frequency of 10(-5) to 10(-7)/PFU. However, we could not detect the transduction of any indigenous virulence plasmid (ca. 72 kb) in pathogenic Yersinia strains. Transductants obtained by infection with the temperate phage were lysogenic and harbored the phage genome in their chromosomes.

Characterization of plasmid regions of foodborne Yersinia enterocolitica biogroup 1A strains hybridizing to the Yersinia enterocolitica virulence plasmid

The aim of our study was to find out if plasmids of foodborne Yersinia enterocolitica biogroup 1A strains harbour genes related to the virulence genes located on the virulence plasmid pYV of Yersinia enterocolitica. The foodborne strains were isolated from pork, as pigs are considered as an important reservoir for enteropathogenic Y. enterocolitica 0:3 and 0:9 strains. The plasmids of the foodborne strains were characterized by restriction enzyme analysis and hybridized to the virulence plasmid pYV of pathogenic Y. enterocolitica strains (0:3 biogroup 4; 0:9 biogroup 2). In several cases the plasmids of the foodborne strains showed homologies to parts of the pYV plasmid. Analysis of the hybridizing regions revealed that genes involved in replication, sequences of transposable elements and an endonuclease gene caused the observed hybridization to the virulence plasmid. In cause of the study also a remnant of a Tn3-like transposon was shown to be present adjacent to the yadA gene on the pYV plasmid. Although there is evidence that at least some strains of Y. enterocolitica biogroup 1A might possess pathogenic properties none of the well known plasmid encoded virulence genes were present on the plasmids of the investigated foodborne biogroup 1A strains.

Plasmids and outer membrane proteins of Yersinia enterocolitica and related species of swine origin

Yersinia enterocolitica and other pathogenic yersiniae harbor a plasmid termed pYV which is required for the full expression of virulence. The pYV codes for the release of a set of proteins called Yops and two outer membrane proteins Yad A and Ylp A. In the present study, 80 strains of Y. enterocolitica and related species were examined for the possession of the pYV and the ability to express Yops and Yad A. Only Y. enterocolitica belonging to serogroups O:1,2,3, O:3, O:5,27, O:8, and O:9 harbored the virulence plasmid and were positive for the presence of the ancillary proteins. The restriction fragment patterns of the pathogenic bioserotypes belonging to the same serogroup affiliation were similar irrespective of whether they were of swine origin, reference strains, or human clinical isolates. The same was also true of the electrophoretic patterns of the Yops. Our findings are in agreement with previous studies and support the view that pigs may be an important reservoir of pathogenic Y. enterocolitica.