Identification of immunogenic proteins associated with protection against haemorrhagic septicaemia after vaccination of calves with a live-attenuated aroA derivative of Pasteurella multocida B:2

Pasteurella multocida serotype B:2 is the causative agent of haemorrhagic septicaemia (HS), a fatal disease of cattle and buffaloes. As a step towards the identification of individual antigens that may protect against HS, proteins present in a sonicated cell extract (SCE) and outer-membrane protein (OMP) preparation of a wild-type P. multocida serotype B:2 were investigated by immunoblotting with sera from calves which had been protected against challenge with a virulent strain of P. multocida B:2 by vaccination with a live-attenuated aroA derivative of the challenge strain. Five proteins in SCE, of approximately 50, 37, 30, 26 and 16 kDa, were recognised by the sera. In an OMP preparation, two bands, at 37 and 50 kDa, were recognised as strongly immunogenic. Mass spectrometry analysis of proteins corresponding in size to those detected by immunoblotting identified the 37 kDa band as OmpA, but the band at 50 kDa was not identified with certainty. A major 30 kDa OMP, identified as OmpH, was not strongly immunogenic.