Cytotoxic effect of Pasteurella haemolytica on ovine bronchoalveolar macrophages in vitro.

Live Pasteurella haemolytica A1 was shown to have a cytotoxic effect on suspensions of sheep bronchoalveolar macrophages. Cytotoxic activity was also demonstrable in bacteria-free supernatants from suspensions containing P. haemolytica. Heat-killed and ultra-violet killed organisms of P. haemolytica and live Staphylococcus aureus were not toxic to sheep BAM. These results suggest that a bacterial cell-free cytotoxin is produced by metabolically active P. haemolytica. Guinea-pig peritoneal macrophages, McCoy and pig kidney epithelial cell suspensions were unaffected by live P. haemolytica and supernatant from P. haemolytica cultures, indicating that the cytotoxin may only affect phagocytic cells of ovine or bovine origin.