Infectivity and virulence of nonpesticinogenic Pasteurella pestis.

Nonpesticinogenic Pasteurella pestis, which is also negative for coagulase and fibrinolytic activities and therefore referred to as (PI-C-F)(-), was investigated to determine whether greatly reduced and erratic lethal responses observed in mice and guinea pigs might be due to inability of the inoculum to establish infection and multiply in survivors. Immunity of survivors was regarded as an indication of previous infection, and, in the case of guinea pigs infected intradermally, appearance of a local lesion and bubo were also noted. Evidence of infection was obtained in most mice and guinea pigs surviving injection of (PI-C-F)(-) strains G-32 and Dodson, suggesting that the virulence determinant (PI-C-F) is related to lethality rather than to infectivity.