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The purpose of the study was the determination of biochemical features of strains belonging to Yersinia genus isolated from clinical material and other sources, and an assessment of the usefulness of certain biochemical tests for the detection of potentially pathogenic Yersinia strains. In all, 110 strains were studied, including 48 from the archives of the National Institute of Hygiene, 38 isolated from food of animal or plant origin, and 24 isolated from blood and faeces of patients. On the ground of the biochemical features the isolated strains were recognized as belonging to 5 species: Y. enterocolitica(83 strains), Y. pseudotuberculosis(12 strains), Y. frederiksenii(7 strains), Y. kristensenii(2 strains) and Y. intermedia(4 strains). Two strains differed in their features from the typical species reveale as yet in Yersinia genus. All strains isolated from clinical material were recognized as Y. enterocolitica, while those isolated from food included also Y. frederiksenii, Y. intermedia and Y. kristensenii. The isolated strains grew well on CIN medium forming characteristic violet-pink colonies with irregular outlines after 24-48 hours of incubation at 25 degrees C or 37 degrees C. The potential pathogenicity was assessed on the basis of the presence of autoagglutination (AA) and absent ability of breaking down of salicin, aesculin and pyrazinamide. Only two strains of Y. enterocolitica 03 isolated from faeces and 5 strains of Y. pseudotuberculosis from the archives had AA ability. Low frequency of AA was explained with possible loss of plasmids conveying virulence as a result of multiple passages of the strains, and the fact that many of them were present in the R phase. All strains of Y. enterocolitica 03 and both Y. enterocolitica 09 strains from the archives could be assumed to be potentially pathogenic for man and animals, while no strain isolated from food showed the set of features which could suggest its possible pathogenicity.

By the method of alkaline lysis the occurrence was studied of plasmid DNA in 122 strains of Yersinia. In 29 strains a single plasmid was found with characteristic growth of the organism on CRMOX (CRMOX+) medium. These features are encoded by genes located on the pYV virulence plasmid. The group of Yersinia strains possessing the virulence plasmid included 27 strains of Y. enterocolitica 0:3 isolated from clinical materials, among them 21 strains isolated from patients between January and September 1996, while the remaining two strains with the virulence plasmid belonged to Y. pseudotuberculosis antigenic group I. Following restriction analysis with the EcoRI enzyme of the virulence plasmids isolated from 27 strains of Y. enterocolitica 0:3 occurrence of only one restriction endonuclease pattern agreeing with the virulence plasmid pattern of Y. enterocolitica 0:3 strains reported in the literature was found in all strains. On the other hand, the restriction analysis of the virulence plasmids obtained from Y. enterocolitica 0:3 and Y. pseudotuberculosis I strains showed evident differences between these plasmids in the size of the particle and the restriction pattern. The plasmid size calculated on the basis of the analysis of the restriction endonuclease patterns for virulence plasmids isolated from the strains of Y. enterocolitica 0:3 and Y. pseudotuberculosis I was 71.5 thousands and 62.7 thousands of base pairs respectively, and was in the range 60-75 thousands bp (40-50 Mda) reported in the literature for virulence plasmids of Yersinia. The study showed that finding of characteristic growth of Yersinia organisms on the CRMOX medium can be useful for the detection of strains containing the pYV virulence plasmid and for the determination of their potential pathogenicity.