Effect of aztreonam on the growth of Pasteurella multocida in the lung.

Specific-pathogen-free ICR mice were infected aerogenically with Pasteurella multocida and, beginning 1 hour later, were treated with aztreonam (50 mg/kg of body weight). The number of viable bacilli in the lungs, liver, and spleen were determined at intervals for up to 36 hours. Aztreonam was bactericidal for growing bacilli in vitro and, when injected 1 and 5 hours after aerogenic exposure, provided greater than 80% protection after dosage at the level of 12.5 mg/kg. Below this dosage level, viable organisms persisted in the lungs and the spleen and many of the minimally treated mice eventually died of pasteurellosis. The survivors developed active immunity as a result of the continued sublethal infection. Aztreonam protects mice against an aerogenic infection with highly virulent P multocida and may be useful in the prevention and treatment of pasteurellosis in cattle.