Cross-protection of mice provided by active and passive immunization against experimental infections with virulent Proteus rettgeri and Providencia bacteria.

Immunization with Providencia and Proteus rettgeri Formalin-treated bacterial suspensions produced high levels of protection in mice against homologous and heterologous challenge. Mice were also cross-protected, but less effectively, by passive administration of rabbit type-specific antisera. The protective activity appeared to be due to an antigen common to strains of different O-serotypes. It was not detectable in agglutination reactions, and preliminary results indicate that it is thermostable, not being inactivated in its antibody binding capacity at 121 degrees C for 1 h.