Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 2013
Publication Date: N/A
Interpretive Summary: Mannheimia haemolytica is a bacterium associated with pneumonia in domestic cattle, sheep, goats and wild bighorn sheep. Multiple serotypes of this bacterium are involved in disease of all affected species. Modified-live M. haemolytica vaccine strains were constructed and two were evaluated in a combination vaccine delivered to sheep and goats. Vaccinated animals were highly resistant to challenge by a combination of virulent strains. The results support the possibility that disease caused by all or most serotypes of M. haemolytica may be preventable using a single dose of modified-live combination vaccine.
Technical Abstract: A temperature-sensitive shuttle vector, pBB80C, was utilized to generate in-frame deletion mutants of the leukotoxin structural gene (lktA) of Mannheimia haemolytica serotypes 1, 2, 5, 6, 7, 8, 9, and 12. Culture supernatants from the mutants contained a truncated protein with an approximate molecular weight of 66 kDa which was reactive to anti-leukotoxin monoclonal antibody. No protein reactive to anti-LktA monoclonal antibody was detected at the molecular weight 100-105 kDa of native LktA. Sheep and goats vaccinated intramuscularly with a mixture of serotypes 5 and 6 mutants were resistant to virulent challenge with a mixture of the wild-type parent strains. These vaccinates responded serologically to both vaccine serotypes and exhibited markedly-reduced lung lesion volume and pulmonary infectious load compared to control animals. Control animals yielded a mixture of serotypes from lung lobes, but the proportion even within an individual animal varied widely from 95% serotype 5 to 95% serotype 6. Cultures recovered from liver were homogeneous, but two animals yielded serotype 5 and the other two yielded serotype 6 in pure culture.