Serological relationship between strains of Pasteurella multocida.

The serological inter-relationships of twenty four strains of Pasteurella multocida represented by 11 reference strains, each representing a different serogroup, and 13 strains from cattle with hemorrhagic septicemia were determined by agglutination and gel diffusion tests. There was agreement between the results of the two procedures indicating that both tests were probably employing the same antigen. Although all strains had strong serogroup-specific agglutinating and precipitating properties, they exhibited varying degrees of cross-reactivity. Strains M4, V A3 and Kobe 6 and strains R473 and 147 showed a close relationship with each other and might be regarded as having the same somatic antigen. Field isolates showed a distribution of reactions about the homologous titers of somatic groups 6, 7 and 8.