|Dassanayake, Rohana -|
|Call, Douglas -|
|Sawant, Ashish -|
|Casavant, Carol -|
|Weiser, Glen -|
|Srikumaran, Subramaniam -|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2009
Publication Date: February 1, 2010
Repository URL: http://aem.asm.org/cgi/reprint/76/4/1008
Citation: Dassanayake, R.P., Call, D.R., Sawant, A.A., Casavant, C.N., Weiser, G.C., Knowles Jr, D.P., Srikumaran, S. 2010. Bibersteinia trehalosi inhibits the growth of mannheimia haemolytica by a proximity-dependent mechanism. Applied and Environmental Microbiology. 76(4):1008-1013. Interpretive Summary: Mannheimia (Pasteurella) haemolytica causes population limited pneumonia in bighorn sheep. Potential sources of this bacterium are bighorn and domestic sheep. These data show that another bacterium, Bibersteinia (Pasteurella) trehalosi commonly found in the upper respiratory tract of bighorn sheep inhibits the growth of M. haemolytica. The inhibition resulted in a 6 to 9 log decrease in growth of this important pathogene (M. haemolytica) in vitro. These data indicate that B. trehalosi may be used to reduce the levels of M. haemolytica in bighorn and domestic sheep and reduce transmission risk.
Technical Abstract: Mannheimia (Pasteurella) haemolytica is the only pathogen that consistently causes severe bronchopneumonia and rapid death of bighorn sheep (BHS; Ovis canadensis) under experimental conditions. Paradoxically, Bibersteinia (Pasteurella) trehalosi and Pasteurella multocida have been isolated from BHS pneumonic lungs much more frequently than M. haemolytica. These observations suggest that there may be an interaction between these bacteria and we hypothesized that B. trehalosi over-grows or otherwise inhibits the growth of M. haemolytica. Growth curves (mono-culture) demonstrated that B. trehalosi has a shorter doubling time (~10 min vs. ~27 min) and consistently achieves 3-log higher cell density (CFU/ml) compared with M. haemolytica. During co-culture M. haemolytica growth was inhibited when B. trehalosi entered stationary phase (6 hr) resulting in a final cell density for M. haemolytica that was 6-9 logs lower than expected with growth in the absence of B. trehalosi. Co-culture supernatant failed to inhibit M. haemolytica growth on agar or in broth indicating no obvious involvement of lytic phages, bacteriocins or quorum sensing systems. This observation was confirmed by limited growth inhibition of M. haemolytica when both pathogens were cultured in the same media but separated by a filter (0.4-µm pores) that limited contact between the two bacterial populations. There was significant growth inhibition of M. haemolytica when the populations were separated by membranes with a pore-size of 8-µm that allowed free contact. These observations demonstrate that B. trehalosi can both outgrow and inhibit M. haemolytica growth with the latter related to a contact- or proximity-dependent mechanism.