IDENTIFICATION OF A POTENTIALLY IMPORTANT ANTIGEN OF PASTEURELLA-HAEMOLYTICA

To identify antigens which may be important for stimulating immunity t o pneumonic pasteurellosis, a bovine antiserum to whole P. haemolytica was used to screen a recombinant lambda gt11/P. haemolytica expressio n library. One of the recombinant bacteriophage clones identified with the bovine antiserum, SW20C, expressed a fusion protein which was als o recognized by rabbit antiserum to partially purified P. haemolytica culture supernatant and was found to be immunogenic in guinea pigs. Th e guinea pig antibody recognized a 100 kDa protein in P. haemolytica c ell lysates. Sequence analysis of the cloned DNA from SW20C identified a fragment of 1446 bp with a small open reading frame that was contig uous with the lacZ sequence. The 153 bp P. haemolytica-specific open r eading frame encoded a polypeptide of approximately 6 kDa. Homology se arches of Genbank and the EMBL data bases revealed no homology of this open reading frame with any other bacterial sequences including P. ha emolytica leukotoxin and Ssa1. Evaluation of sera from calves that wer e scored either susceptible or resistant to experimental pneumonic pas teurellosis demonstrated a significant (P < 0.001) correlation between the intensity of the antibody response to the SW20C antigen and resis tance to disease.