Evaluation of virulence factor testing and characteristics of pathogenicity in Yersinia enterocolitica

The virulence of 10 strains of Yersinia enterocolitica containing 42- to 44-megadalton plasmids (serogroups O:3; O:4,32; O:8; O:9; O:13,7; and O:21) was compared in mice and guinea pigs. Adult mice were more responsive than guinea pigs to the Sereny-like conjunctivitis test. In tests on suckling mice, all Yersinia strains harboring plasmids were lethal, whereas all strains without plasmids were nonlethal. All strains of serogroups O:4,32; O:8; O:13,7; or O:21 which harbored a plasmid gave positive results in the mouse Sereny, peroral, and intraperitoneal tests. A positive reaction in these tests was correlated with the ability of the strains to elaborate lipase. Because the Sereny, peroral, and intraperitoneal tests measured the same virulence factor(s), the findings in any of these three tests would accurately predict the results of the other two tests. Mice which survived the Sereny and peroral tests were subsequently challenged intraperitoneally with 1,000 mouse lethal doses of the virulent WA (O:8) strain. Those inoculated with plasmid-harboring strains were protected, whereas those inoculated with plasmid-free strains were not.