Pasteurella multocida Virulence Factors: Selection of Fowl Cholera-Inducing and Non-Inducing Strains

Relatively little information is available on Pasteurella multocida virulence factors involved in producing fowl cholera. Because of the complex nature of bacterial pathogenesis, the recommended approach for ascertaining these factors is to compare biological attributes of high- and low-virulence strains. To permit use of this approach for fowl cholera, P. multocida strains of high and low virulence were identified. Turkey poults were exposed intrapharyngeally and intravenously (IV) to two antigenically and biochemically similar strains. Based on mortality, strain P-1059 was highly virulent and strain P-1062 was avirulent. Microbiological examination indicated that only the virulent strain infected the pharyngeal mucosa of intrapharyngeally exposed poults and survived and multiplied in IV-exposed poults. These findings indicate strain differences in those virulence factors concerned with the colonization and multiplication stages of disease development.