Role of the virulence-associated plasmids of Yersinia enterocolitica on its immunogenicity against Y. pestis.

Forty-two strains selected from various serovars of Yersinia enterocolitica were studied for their ability to induce cross-protection against Y. pestis. Only primo-infected mice (i.v.) with inocula prepared from strains of Y. enterocolitica belonging to serovars 0:3, 0:9 and 0:5, 27 harbouring a 47-Mdal virulence-associated plasmid were resistant to Y. pestis. The spontaneously cured (plasmid-less) derivatives of these strains had lost the capacity to induce this cross-immunity.