Pathogenicity and immunogenicity of native and mutant strains of Pasteurella multocida, the causative agents of haemorrhagic septicaemia

Haemorrhagic septicaemia (HS) is a fatal systemic disease of cattle and buffaloes. Some control is achieved with administration of alum-precipitated or oil-adjuvanted killed whole-cell vaccines injected subcutaneously. These vaccines, however, provide only short-term immunity and for effective use, they should be administered annually. We constructed an aroA attenuated derivative of a Pasteurella multocida serotype B:2 strain by allelic exchange of the native aroA sequence with aroA sequences disrupted with a kanamycin resistance cassette. This strain was confirmed to be aroA mutant by peR. The aroA derivative was highly attenuated for virulence in a mouse model of HS and rabbits. Mouse and rabbit challenge experiments showed that i.p, or i.m. vaccination of an arcA strain completely protected mice or rabbits against challenge with a high dose ( 1000 LD,,) of the parent strain.