Bacterial multiplication in the lung associated with murine Sendai virus pneumonia is caused by virus-induced defects in pulmonary bactericidal mechanisms. The nature of this effect has been studied in animals immunized against the challenge bacteria. Mice were immunized against Proteus mirabilis by intraperitoneal inoculation and by aerosol inhalation. After the development of immunity, mice were infected aerogenically with 104 TCID50 of Sendai virus. 7 days later, during the height of the bronchial inflammation and pulmonary consolidation, the mice were challenged with an aerosol of viable 35S-labeled Proteus mirabilis or 32P-labeled Staphylococcus aureus.
