Diagnostic value of plasmid analyses and assays for virulence in Yersinia enterocolitica.

The possession of a 42- to 48-megadalton plasmid alone does not appear to be predictive of virulence in Yersinia species. Twelve of 100 Yersinia enterocolitica strains contained a 42 to 48-megadalton plasmid, and 4 of 30 Y. enterocolitica-like strains contained a 42- to 48-megadalton plasmid. Seven strains of Y. enterocolitica contained the 42- to 48-megadalton plasmid plus an 82-megadalton plasmid, and these were the only study strains lethal for mice. Based on restriction endonuclease digestion, the 42- to 48-megadalton plasmid DNA from these seven strains were similar and were not similar to the 42- to 48-megadalton plasmids present in the other nine strains. The ability to invade guinea pig eye tissues, calcium dependency, autoagglutination, and colonial morphology at 37 degrees C were also associated with plasmid DNA, but the relationships were either variable or not reciprocal. Neither tissue culture invasiveness nor heat-stable toxin production was associated with plasmid DNA. It was concluded that biochemical speciation and a total plasmid profile in combination with enzyme digests are predictive of virulence in Y. enterocolitica as it is measured by mouse lethality.