Experimentally induced pneumonia in scid/beige mice, using a bovine isolate of Pasteurella haemolytica

Intranasal challenge of immunocompetent mice with Pasteurella haemolytica results in little or no pulmonary inflammation. The study reported here was designed to investigate the inflammatory response in the lungs of immunodeficient scid/beige mice after similar challenge.

Fifty-five scid/beige mice were challenged intranasally with saline or one of three doses (2.8 x 10(6), 3.4 x 10(9), or 3.3 x 10(11) colony-forming units [CFU]/ml) of P. haemolytica. The lungs were examined for changes in weight, bacterial count, and presence of gross and microscopic lesions at 24, 48, or 96 hours after challenge.

Intranasal challenge with concentrations > or = 3.4 x 10(9) CFU/ml of P. haemolytica induced significantly heavier lung weight, with severe pulmonary lesions, and development of suppurative and fibrinous bronchopneumonia in dose- and time-dependent manner 48 hours after challenge. Pasteurella haemolytica was consistently isolated from the lungs at 24 hours after challenge.

Bronchopneumonia was induced by P. haemolytica in mice without manipulation of the mouse or the bacteria. The lesions were similar to those that develop in the lungs of cattle infected with P. haemolytica and indicate potential use of the model for the study of this host/bacterial interaction.