[Microbiology and epidemiology of Yersinia infections]

Eleven species are actually recognized within the genus Yersinia of which three--Y. pestis, Y. pseudotuberculosis, and certain serovars of Y. enterocolitica--are important infectious organisms for humans and warm-blooded animals. The causative agents of yersiniosis, Y. pseudotuberculosis and Y. enterocolitica, occur world-wide in areas of moderate and subtropical climate. Asymptomatically infected warm-blooded animals, causing environmental contamination, are the most important factors for the epidemiology of yersiniosis; apathogenic Yersinia species and serovars, on the other hand, are largely adapted to environmental conditions and, with regard to their ecology, independent from warm- or cold-blooded host organisms. The agents are usually transmitted by the oral route with food-stuffs as the most important vehicle of human yersiniosis. For their isolation, enrichment procedures and selective media have been developed. The organisms are identified by biochemical reactions and can be differentiated by serological and, in case of Y. enterocolitica, also by phage-typing methods. The differentiation of pathogenic and apathogenic strains is of diagnostic importance and should be routinely performed; simple tests are available for this purpose. Demonstration of antibodies against cell-wall-associated (lipopolysaccharide) or plasmid-encoded (protein) antigens may confirm the diagnosis if the causative agents failed to be isolated.