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

Background and Purpose: Intranasal challenge of immunocompetent mice with P asteurella haemolytica results in little or no pulmonary inflammation. The study reported here was designed to investigate the inflammatory response i n the lungs of immunodeficient scid/beige mice after similar challenge. Methods: Fifty-five scid/beige mice were challenged intranasally with salin e or one of three doses (2.8 x 10(6), 3.4 x 10(9), or 3.3 x 10(11) colony-f orming units [CFU]/ml) of P, haemolytica. The lungs were examined for chang es in weight, bacterial count, and presence of gross and microscopic lesion s at 24, 48, or 96 hours after challenge. Results: Intranasal challenge wit h concentrations greater than or equal to 3.4 x 10(9) CFU/ml of P. haemolyt ica induced significantly heavier lung weight, with severe pulmonary lesion s, and development of suppurative and fibrinous bronchopneumonia in dose- a nd time-dependent manner 48 hours after challenge. Pasteurella haemolytica was consistently isolated from the lungs at 24 hours after challenge. Conclusions: Bronchopneumonia was induced by P. haemolytica in mice without manipulation of the mouse or the bacteria. The lesions were similar to tho se that develop in the lungs of cattle infected with P. haemolytica and ind icate potential use of the model for the study of this host/bacterial inter action.