A comparison of Pasteurella multocida isolated from healthy cattle and cattle with shipping fever

Nasal swabs from 300 apparently healthy calves and dairy cows were cultured on bovine blood agar medium. Nine isolates of Pasteurella multocida and three isolates of Pasteurella hemolytica were recovered. Using similar cultural procedure three isolates of P. multocida and two of P. hemolytica were recovered from cattle with shipping fever. The colonial morphology, antigenic type staining reactions and biochemical properties of each isolate of P. multocida were determined. The isolates were typed by the indirect hemagglutination test employing the technique of Carter 7, 9 using human type 0 erythrocytes. Of the 9 isolates of Pasteurella multocida from healthy animals 5 were type A, 2 were type B and 2 could not be typed. All 3 isolates from cattle with shipping fever were type A. The pathogenicity of each isolate was determined in white mice. Tenfold dilutions of a 24 hour culture were injected intraperitoneally (0.2 ml per mouse) and the MLD₅₀ were calculated. The cultural and biochemical properties, the pathogenicity and other characteristics of P. multocida isolates from healthy animals and from animals with shipping fever were compared with each other and with the known types (Carter's A, B, C and D). No statistically significant difference of pathogenicity was demonstrated between P. multocida isolates from healthy animals and from animals with shipping fever, between known types and isolates from animals with shipping fever, and between known types and isolates from healthy animals. The biochemical and cultural properties of the isolates and the known types were indistinguishable