Yersinia enterocolitica in milk and dairy products.

Yersinia enterocolitica was first recognized during the 1960's as an important human enteropathogen. The species as later redefined includes both pathogenic and nonpathogenic forms. Pathogenic strains that retain the virulence plasmid can be identified in several animal models and four indirect tests (calcium dependency, autoagglutination, Congo red uptake, serological detection of outer membrane antigen) and by tissue culture assay, serotype, and biotype. Y. enterocolitica and related bacteria have frequently been isolated from raw milk, but none of the isolates, with the possible exception of serotype 05,27, are recognizable as pathogens. Under normal circumstances Y. enterocolitica does not survive pasteurization. If introduced into pasteurized milk, it can grow well at refrigeration temperatures. Two outbreaks of yersiniosis have occurred that involved pasteurized milk. Pigs, which frequently carry pathogenic Y. enterocolitica in their throat, were the probable source in one of these outbreaks. The most rapid enrichment procedure available for isolation of Y. enterocolitica requires 6 d. No isolation method is available for selective isolation of pathogenic Y. enterocolitica in the presence of related bacteria common in milk and other foods.