Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2012
Publication Date: May 1, 2012
Citation: Briggs, R.E., Tabatabai, L.B., Tatum, F.M. 2012. Mucosal and parenteral vaccination against pneumonic pasteurellosis in cattle with a modified-live in-frame lktA deletion mutant of Mannheimia haemolytica. Microbial Pathogenesis. 52(5):302-309. Interpretive Summary: A new temperature-conditional plasmid shuttle vector was constructed and utilized to generate a deletion mutant of the bacterium Mannheimia haemolytica, an important causative agent of bovine respiratory disease. The mutant organism no longer produced active leukotoxin, a pivotal virulence factor for the organism, but instead produced a shorter form of inactive leukotoxin effective at inducing immunity. Vaccination by conventional injection, or by applying the live bacteria on cattle feed, effectively made calves resistant to virulent M. haemolytica. Antibody response, reduction in lung lesions, and reduction in infectious load was greater among calves fed the vaccine than those which were injected.
Technical Abstract: A new temperature-conditional shuttle vector, pBB80C, was constructed and utilized to generate an in-frame deletion in the leukotoxin structural gene of Mannheimia haemolytica serotype 1. Culture supernatants from the mutant contained no detectable cytotoxicity to BL-3 lymphocyte targets, and contained a new protein of approximately 66 kDal MW which was reactive to anti-leukotoxin monoclonal antibody. No protein reactive to anti-LktA monoclonal antibody was detected at the 100-105 kDal MW of native LktA. Calves vaccinated mucosally by top-dressing the live mutant onto feed, or parenterally by subcutaneous injection, were resistant to virulent challenge with the parent strain. Serologic antibody response, reduction in lung lesion, and reduction in pulmonary infectious load was greater among calves mucosally vaccinated than those which were vaccinated by injection.