THE ISOLATION OF RECOMBINANT PLASMIDS EXPRESSING SECRETED ANTIGENS OFPASTEURELLA-HAEMOLYTICA-A1 AND THE CHARACTERIZATION OF AN IMMUNOGENIC60-KDA ANTIGEN

A collection of recombinant plasmids had been isolated which express s ecreted antigens of Pasteurella haemolytica A1 likely to be important in protection. The recombinant Escherichia coli clones were found to e xpress the. haemolytica A1 antigens by Western immunoblot analysis, us ing sera from calves which had been vaccinated with Presponse(TM) and were subsequently resistant to experimental challenge with P. haemolyt ica A1. Detailed analysis of three of the recombinant plasmids (pGS1-1 7, pGS3-19 and pSA1-50) showed that they all carry the same 4.2 kbp in sert DNA, E. coli clones which carry the recombinant plasmids all expr ess a strongly antigenic protein of approximately 60 kDa. Nucleotide s equence analysis of the cloned DNA showed that it codes for a polypept ide with an estimated M.W. of 60.8 kDa. A partial clone of this gene h as been reported previously and an antibody response to the antigen wa s shown to be significantly correlated to resistance to disease. This gene was found to be present in only the A biotypes of P. haemolytica and not in the T biotypes, which have been reclassified Pasteurella tr ehalosi. This demonstrates that this recombinant plasmid collection co des for antigens of P. haemolytica A1 important to protection and warr ants further characterization to identify additional recombinant antig ens.