Protection against Yersinia infection induced by non-virulence-plasmid-encoded antigens.

Specific immunity against Yersinia was induced by plasmid-encoded antigens not associated with virulence. Mice were immunised with viable bacteria from a virulence-plasmid-cured strain of Y. pseudotuberculosis. This antigenic stimulation generated specific protection against virulence-plasmid-harbouring strains of Y. pseudotuberculosis and Y. pestis, demonstrating that protection can be generated by organisms lacking plasmid-encoded virulence antigens.