Pasteurella multocida produces a protein with homology to the P6 outer membrane protein of Haemophilus influenzae.

An antibody specific for a 16-kDa outer membrane protein of a rabbit strain of Pasteurella multocida was used to probe representatives of all 16 somatic serotypes of P. multocida, as well as the vaccine strains CU and M9, and all were shown to express the protein. The gene encoding this protein was cloned and sequenced and found to have extensive sequence homology with the gene encoding the P6 protein of Haemophilus influenzae. The protein in P. multocida has been designated P6-like. The gene encoding the P6-like protein was used to probe members of the family Pasteurellaceae and other gram-negative bacteria. Representatives of all 16 somatic serotypes (as well as the vaccine strains CU and M9) of P. multocida hybridized with the P6-like gene under conditions of high stringency. The DNA from H. influenzae hybridized weakly with the P6-like gene under these conditions, but Pasteurella haemolytica (representatives of A and T biotypes), Bordetella bronchiseptica, B. avium, Actinobacillus suis, A. suis-like, A. lignieresii, A. ureae, A. rossii, A. pleuropneumoniae, A. equuli, and various members of the family Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium) did not hybridize detectably. Under conditions of lower stringency, the P6-like gene also hybridized strongly with DNA from P. multocida, H. influenzae, and A. rossii but weakly with DNA from P. haemolytica and members of the genus Actinobacillus. These results suggest that the P6-like protein of P. multocida might be useful as an immunizing product to protect poultry from avian cholera. This suggestion stems from (i) our finding that the P6-like protein in P. multocida is widely distributed among all the somatic serotypes and (ii) the previous work of others demonstrating that the P6 protein of H. influenzae elicits a protective immune response in animal models of human disease.