Studies of lung infections caused by Pseudomonas aeruginosa in mice treated with cyclophosphamide.

An experimental Pseudomonas aeruginosa lung infection was induced by aerosol exposure in mice which had been pretreated with cyclophosphamide. A single dose of 200 mg/kg cyclophosphamide resulted in leukopenia which lasted for three days. At the lowest PMN levels, the mice were exposed to aerosols containing varying doses of bacteria. The survival time of the mice and the number of viable bacteria in their lungs were determined. A dramatic rise in the viable counts of Pseudomonas organisms was found between 18 and 24 hours after infection. Mice which had not been pretreated with cyclophosphamide remained healthy and did not show any lung lesions. The number and phagocytic function of the alveolar macrophages remained unaltered after cyclophosphamide treatment. Thus, PMNs seem to play an important role in the lung's early defence mechanisms against Pseudomonas aeruginosa. This animal model could be of use in evaluating additional therapies for lung infections caused by Pseudomonas aeruginosa.