Cloning of a serotype-specific antigen from Pasteurella haemolytica A1

Recombinant plasmids coding for a soluble (or surface) antigen of Pasteurella haemolytica A1 were identified. Two plasmids, both containing the same 5.4 kilobase pairs of insert DNA, were recovered independently by screening a clone band of P. haemolytica A1 genomic DNA in Escherichia coli for the expression of P. haemolytica A1 soluble antigens (R. Y. C. Lo and L.A. Cameron, Can. J. Biochem. Cell Biol. 64:73-76, 1986). E. coli cells carrying the plasmids were found to be agglutinated by an antiserum raised against the P. haemolytica A1 soluble antigens. Analysis of the E. coli clones by electron microscopy revealed patches of amorphous material on the surface of the cells which were not present on the controls. Further characterization with protein A-colloidal gold labeled both these patches and the outer membranes of these cloned cells pretreated with the specific antiserum. These results indicated that the cloned antigen was expressed on the surface of the E. coli cells. The cloned antigen was found to be specific for serotype 1 when tested by slide agglutination against a collection of P. haemolytica typing antisera. Southern blot hybridization, using the cloned DNA as a probe, labeled the genomic DNA from P. haemolytica serotype 1 as well as the cross-agglutinating serotypes 2 and 7, but not DNA from the non-cross-agglutinating serotypes 3 and 4 and Pasteurella multocida. These results demonstrated that serotype specificity could be attributed to the particular antigenic determinants in the genome of the organism.