|Knowles, Donald - Don|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2009
Publication Date: 2/1/2010
Publication URL: http://aem.asm.org/cgi/reprint/76/4/1008
Citation: Dassanayake, R.P., Call, D.R., Sawant, A.A., Casavant, N.C., 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: Pneumonia is a population limiting disease in big horn sheep. Abundant experimental evidence points to Mannheimia (Pasteurella haemolytica) as a major contributor to pneumonia in big horn sheep. Due to the presence of Pasteurella sp. in big horn sheep and domestic livestock methods to limit the carry state and transmission are needed. These data report the finding that Bibersteinia (Pasteurella) trehalosi inhibits the growth of Pasteurella haemolytica by a contact-dependent mechanism. These findings suggest a scenario whereby P. haemolytica isolation from pneumonic lungs is limited by inhibition by P. trehalosi and indicates P. trehalosi may have utility as a broader inhibitor of growth and colonization of P. haemolytica.
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 occasionally 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. Therefore, we hypothesize that B. trehalosi inhibits the growth of M. haemolytica. Co culture of B. trehalosi with M. haemolytica revealed that although M. haemolytica growth was not significantly affected up to six hours of co-culture, growth slowed thereafter, with a rapid decline (~6-9 logs CFU/ml) occurring from 12 h to 24 h (compared to mono-cultures) indicating that B. trehalosi inhibits the growth of M. haemolytica. Co-culture supernatant fluid failed to inhibit M. haemolytica growth on agar or in broth indicating no evidence for lytic phages or secreted growth inhibitors. This observation was confirmed by the absence of growth inhibition of M. haemolytica when both pathogens were cultured in the same media but separated by a membrane (0.4-µm pores) that prevented contact between the two bacterial species. There was significant growth inhibition of M. haemolytica when the populations were separated by membranes with a pore-size of 8-µm that allowed contact between the two species. These observations demonstrate that B. trehalosi-induced inhibition of M. haemolytica growth is mediated by a contact-dependent mechanism and this could be a contributing factor for limited recovery of M. haemolytica from BHS pneumonic lungs.