Attenuated Live Fowl Cholera Vaccine I. Development of Vaccine Strain M3G of Pasteurella multocida

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Abstract
A live cholera vaccine was developed from a virulent avian septicemia strain of P. multocida serotype 1. The virulent parental strain was mutagenized with N-methyl-N''-nitro-N-nitroso guanidine. Mutants were selected that had smaller colonies at 37.degree. C or temperature sensitivity for growth at 41.degree. C. Four small-colony mutants and 2 temperature-sensitive mutants were studied. All the mutants were avirulent for turkeys. Sixteen days after turkeys were vaccinated with each mutant, vaccinated and unvaccinated controls were challenge-exposed to virulent P. multocida of the homologous serotype and the heterologous serotype 3. Of the small-colony mutant strains, 2 protected against homologous and heterologous challenge. Suggested for a live cholera vaccine is P. multocida M3G, a small-colony-forming mutant, innocuous for mice and turkeys and stable against reversion.