[Plasmid-mediated pathogenicity factors of Yersinia enterocolitica from the epidemiological viewpoint]

In an attempt to evaluate the epidemiological significance of Y. enterocolitica strains isolated from domestic animals with latent infections, i.e. from swine (31), dogs (9), cats (2), and the environment (2) were compared, in respect of their pathogenic properties, with reference strains (27) from human patients. The results did not contradict the assumption of animals being a source of human infections. In general, these strains of the serovars 0:3 and 0:9 possessed a virulence plasmid with a molecular weight of 46 Mdal (+/- 3 Mdal), irrespective of their origin from humans or domestic animals with latent infections. There was a consistent correlation of the presence of the virulence plasmid and of positive reactions in Laird's and Cavanaugh's autoagglutination test (1980) (Tab. 1): The strains harbouring this plasmid were calcium dependent on MOX agar (18) as well. These strains were capable of colonizing the intestine of mice in a modified mouse diarrhea model (Fig. 1). In these latently infected mice low titers of species-specific antibodies were detected. It was possible to select plasmid harbouring substrains out of heterogenic strains, which had undergone conversion to plasmidless isogenic variants when applying the modified mouse diarrhea model. In a newly developed "macrophage-virulence-test", strains harbouring the virulence plasmid were able to multiply within the macrophage of mice (Fig. 4, 5) with cytopathogenic effects. In a modified Sereny-test European strains of the serovars 0:3 and 0:9 were shown to be invasive in the conjunctival epithelium of guinea pigs' eyes as an additional plasmid-associated property (Fig. 3). European strains of atypical biochemical or serological patterns (among them Y. intermedia, Y. frederiksenii) as well as some strains of the serovars 0:3 and 0:9 did not harbour the virulence plasmid. These plasmidless strains were altogether negative regarding the pathogenic properties mentioned above. Long-term in vitro subcultivation of strains correlated well with the frequency of plasmidless strains: isolates cultivated for a number of years, in contrast to newly isolated strains, hardly harboured virulence plasmis.