Vacuolating cytotoxic activity of Pasteurella multocida causing haemorrhagic septicaemia in buffalo and cattle.

The toxic activity of Pasteurella multocida strains which cause haemorrhagic septicaemia (HS) in buffalo and cattle was examined in a mouse model. Mice were injected intraperitoneally with 10(2) cells of P. multocida serotype B:2,5. Electron microscopy of peritoneal macrophages obtained 6 h after injection revealed strong induction of cytoplasmic vacuolation, macrophage lysis and death. In vitro experiments with the mouse macrophage cell line RAW 264 incubated with cultures of various HS- and non-HS-associated strains of P. multocida or with culture supernatants revealed macrophage vacuolation when HS-associated strains were used. On pre-incubation of the strains with antiserum obtained from buffalo infected with P. multocida serotype B:2,5 no vacuolation was observed. These results are indicative of the presence of vacuolating cytotoxic activity in HS-associated strains of P. multocida.