Assessment of plasmid profile, exoenzyme activity, and virulence in recent human isolates of Yersinia enterocolitica.

We examined a group of 23 recent clinical isolates of Yersinia enterocolitica recovered from symptomatic patients residing in the New York, N.Y. area. These isolates were tested for the presence of plasmids, exoenzyme activity, mouse lethality, and phenotypic properties postulated to correlate with virulence. Of the 23 isolates, 17 harbored a 60- to 65-kilobase (kb) plasmid. Six isolates were lethal for white mice, showed the phenotypic markers of autoagglutination and calcium dependence for growth at 37 degrees C, and contained a 60- to 65-kb plasmid. Restriction endonuclease analysis with several different enzymes revealed the presence of three distinct plasmid profiles in these isolates. Isolates with a single plasmid of 60 to 70 kb, typical for this species, were detected, but these were of three distinct types as judged from restriction enzyme digestion. One strain was unusual among clinical isolates of Y. enterocolitica in that it contained at least four distinct plasmids. In addition, this nontypable strain showed exoenzymatic activity similar to that of serogroup O8 isolates, was not lethal to mice, and did not require calcium for growth at 37 degrees C.