Effects of interactions between Pasteurella haemolytica and Bordetella parapertussis on in vitro phagocytosis by lung macrophages

The aim of the work was to determine the effect of exposing ovine bronchoalveolar macrophages (BAM) in vivo to Pasteurella haemolytica and/or Bordetella parapertussis on the subsequent uptake and killing of P. haemolytica by these cells in vitro. Exposure in vivo to P. haemolytica did not affect the uptake of P. haemolytica by BAM in vitro but reduced (P < 0.05) the intracellular killing of bacteria. Exposure in vivo to B. parapertussis had no significant effect on either the uptake or killing of P. haemolytica in vitro. However, sequential exposure in vivo to B. parapertussis and P. haemolytica reduced both the ingestion (P < 0.05) and killing (P < 0.001) of P. haemolytica in vitro. These results indicate that exposure to P. haemolytica compromised the bacterial killing mechanisms of BAM and that synergy between B. parapertussis and P. haemolytica reduced the ability of BAM to ingest bacteria.