|BAVANANTHASIVAM, JEGARUBEE - Washington State University|
|DASSANAYAKE, ROHANA - Washington State University|
|KUGADAS, ABIRAMI - Washington State University|
|SHANTHALINGAM, SUDARVILI - Washington State University|
|CALL, DOUGLAS - Washington State University|
|Knowles Jr, Donald|
|SRIKUMARAN, SUBRAMANIAM - Washington State University|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2012
Publication Date: 9/1/2012
Citation: Bavananthasivam, J., Dassanayake, R.P., Kugadas, A., Shanthalingam, S., Call, D.R., Knowles Jr, D.P., Srikumaran, S. 2012. Proximity-dependent inhibition of growth of mannheimia haemolytica by pasteurella multocida. Applied and Environmental Microbiology. 78(18):6683-6688.
Interpretive Summary: Mannheimia haemolytica is a bacterium that has been shown to cause fatal pneumonia in bighorn sheep (BHS) under experimental conditions, and approaches to reduce its growth might be used to reduce pneumonia in BHS. We hypothesized that the growth of M. haemolytica in BHS lungs is inhibited by other bacteria like Pasteurella multocida, and we tested this by growing bacteria separately, together, and separated by membranes with varying size openings. Although M. haemolytica and P. multocida showed similar growth when cultured separately, when grown together there was clear inhibition of the growth of M. haemolytica. This inhibition was also observed when the bacteria were separated by a membrane with pores large enough to allow contact, but not with smaller pore sizes that prevented bacterial contact. If present, small secreted compounds or viruses might have been transmitted between P. multocida and M. haemolytica to cause growth inhibition, but none were detected under these conditions. We concluded P. multocida inhibited the growth of M. haemolytica either by direct contact or by very close proximity. Further study of the mechanisms underlying this growth inhibition could lead to treatments to restrict the growth of harmful bacteria and reduce BHS pneumonia.
Technical Abstract: Mannheimia haemolytica, Pasteurella multocida, and Bibersteinia trehalosi have been identified in the lungs of pneumonic bighorn sheep (BHS; Ovis canadensis). Of these pathogens, M. haemolytica has been shown to consistently cause fatal pneumonia in BHS under experimental conditions. However, M. haemolytica has been isolated by culture less frequently than the other bacteria. We hypothesized that the growth of M. haemolytica is inhibited by other bacteria in the lungs of BHS. The objective of this study was to determine whether P. multocida inhibits the growth of M. haemolytica. Although in monoculture both bacteria exhibited similar growth characteristics, in coculture with P. multocida there was a clear inhibition of growth of M. haemolytica. The inhibition was detected at mid-log phase and continued through the stationary phase. When cultured in the same medium, the growth of M. haemolytica was inhibited when both bacteria were separated by a membrane that allowed contact (pore size, 8.0 um) but not when they were separated by a membrane that limited contact (pore size, 0.4 um). Lytic bacteriophages or bactericidal compounds could not be detected in the culture supernatant fluid from monocultures of P. multocida or from P. multocida-M. haemolytica cocultures. These results indicate that P. multocida inhibits the growth of M. haemolytica by a contactor proximity-dependent mechanism. If the inhibition of growth of M. haemolytica by P. multocida occurs in vivo as well, it could explain the inconsistent isolation of M. haemolytica from the lungs of pneumonic BHS.