Inhibition of the growth of Mannheimia haemolytica by other gram negative bacteria

Jegarubee Bavananthasivam

Mannheimia haemolytica, Pasteurella multocida, Bibersteinia trehalosi, and Mycoplasma ovipneumoniae have been identified in the pneumonic lungs of BHS. Although M.haemolytica is a pathogen that consistently causes fatal pneumonia in BHS under experimental conditions, it is isolated by culture much less frequently. The first hypothesis of this study is that the growth of M.haemolytica is inhibited by other bacteria in BHS lungs. Previous studies in our laboratory have demonstrated that B.trehalosi inhibits the growth of M.haemolytica in vitro. The objective of this study was to determine whether P.multocida inhibits the growth of M.haemolytica. When both bacteria were cocultured, there was a clear inhibition of growth of M.haemolytica, which began at mid-log phase and continued through stationary phase. When cultured in the same medium, growth of M.haemolytica was inhibited when both bacteria were separated by a membrane that allowed contact, but not when separated by a membrane that limited contact. These results indicate that P.multocida inhibits the growth of M.haemolytica by a proximity-dependent mechanism. The second hypothesis of this study was that intranasal administration of P.multocida or B.trehalosi will eliminate M.haemolytica from the nasopharynx of DS. Leukotoxin-negative B.trehalosi does not cause pneumonia in BHS. Therefore, the second objective of this study was to determine whether intranasal administration of Lkt-negative B.trehalosi eliminates M.haemolytica from the nasopharynx of DS. Coculture of B.trehalosi and M.haemolytica followed by PCR assay for leukotoxin gene, transformation assay, and electroporation assay revealed the lack of competence of B.trehalosi to acquire exogenous DNA. Intra-nasal administration of leukotoxin-negative B.trehalosi into DS previously colonized with gfp-tagged leukotoxin-positive M.haemolytica, resulted in reduction of M.haemolytica in nasal and pharyngeal secretions. Unexpectedly, E.coli administered to control animals also reduced the number of M.haemolytica, although the reduction was not statistically significant. Coculture of E.coli with M.haemolytica revealed that E.coli also inhibits the growth of M.haemolytica. Hence the in vivo inhibition studies need to be repeated with another bacterium that does not inhibit the growth of M.haemolytica in vitro. Nevertheless, this strategy represents a potential tool to prevent transmission of leukotoxin-positive M.haemolytica from DS to BHS, which has been incriminated in BHS die offs

Inhibition of the growth of Mannheimia haemolytica by other gram negative bacteria

Files and links (1)

Abstract

Metrics

Details