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 isachieved with administration of alum-precipitated or oil-adjuvanted killed whole-cell vaccines injectedsubcutaneously. These vaccines, however, provide only short-term immunity and for effective use, theyshould be administered annually. We constructed an aroA attenuated derivative of a Pasteurella multocidaserotype B:2 strain by allelic exchange of the native aroA sequence with aroA sequences disrupted with akanamycin resistance cassette. This strain was confirmed to be aroA mutant by PCR. The aroA derivativewas highly attenuated for virulence in a mouse model of HS and rabbits. Mouse and rabbit challengeexperiments showed that i.p. or i.m. vaccination of an aroA strain completely protected mice or rabbitsagainst challenge with a high dose (>1000 LD50) of the parent strain.