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Proximity-dependent inhibition of growth of Mannheimia haemolytica by Pasteurella multocida

Jegarubee Bavananthasivam1, Rohana P Dassanayake, Abirami Kugadas

  • 1Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA.

Applied and Environmental Microbiology
|July 17, 2012
PubMed

Insights

Pasteurella multocida inhibits the growth of Mannheimia haemolytica in bighorn sheep lungs. This contact-dependent inhibition may explain why M. haemolytica is infrequently isolated from pneumonic sheep.

Area of Science:

  • Veterinary Microbiology
  • Animal Pathology

Background:

  • Mannheimia haemolytica, Pasteurella multocida, and Bibersteinia trehalosi are lung pathogens in pneumonic bighorn sheep (Ovis canadensis).
  • M. haemolytica experimentally causes fatal pneumonia in bighorn sheep, yet is inconsistently isolated.
  • This suggests potential interbacterial growth inhibition within the host lung environment.

Purpose of the Study:

  • To investigate the hypothesis that other bacteria inhibit M. haemolytica growth in bighorn sheep lungs.
  • Specifically, to determine if Pasteurella multocida inhibits the growth of Mannheimia haemolytica.

Main Methods:

  • Comparative growth studies of M. haemolytica and P. multocida in monoculture and coculture.
  • In vitro experiments using transwell systems with varying membrane pore sizes (8.0 μm vs. 0.4 μm) to assess contact-dependent inhibition.
  • Analysis of culture supernatants for lytic bacteriophages or bactericidal compounds.

Main Results:

  • Both M. haemolytica and P. multocida showed similar growth in monoculture.
  • Coculture with P. multocida significantly inhibited M. haemolytica growth from mid-log to stationary phase.
  • Inhibition occurred when bacteria were separated by a 8.0 μm membrane (allowing contact) but not by a 0.4 μm membrane (limiting contact).
  • No lytic phages or bactericidal compounds were detected in culture supernatants.

Conclusions:

  • Pasteurella multocida inhibits the growth of Mannheimia haemolytica through a contact- or proximity-dependent mechanism.
  • This in vitro finding provides a potential explanation for the inconsistent isolation of M. haemolytica from pneumonic bighorn sheep in vivo.

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