Population genetics of human, animal, and environmental Yersinia strains.

Multilocus enzyme electrophoresis was used to analyze 244 strains of nine Yersinia species isolated from the environment, animals, and humans at 18 genes encoding metabolic enzymes. All 18 enzymes were polymorphic. Among the 137 electrophoretic types (ETs) distinguished, the mean allelic diversity per locus was 0.531. Yersinia frederiksenii ETs were divided into three major clusters that were separated by a large genetic distance, and one ET was more closely related to Yersinia enterocolitica. Thus, strains classically identified as Y. frederiksenii may represent more than one species. Furthermore, two strains identified as Yersinia kristensenii proved to be more closely related to Yersinia mollaretii. Environmental strains formed independent groups. A very interesting ET consisting of as many as 61 isolates of Yersinia enterocolitica was detected, and the epidemiologic relevance of this ET is discussed. Human strains of Y. enterocolitica biotype 4 and Yersinia pseudotuberculosis were recognized as being closely related to animal strains of the same species. Therefore, animal strains of these two species may be considered potential human pathogens.