Lung Bacterial Clearance in Murine Pneumococcal Pneumonia

Publisher Website
Google Scholar
Abstract
The bactericidal capacity of the rat lung was studied during the development of pneumococcal pneumonia. Pneumonia was produced in a lower lobe by the intrabronchial instillation of 104 Streptococcus pneumoniae cells in buffer. Lung bacterial counts progressively increased, reaching 107/lung within 48 h, and the increase was associated with localized atelectasis and consolidation. Bacterial multiplication was inhibited with tetracycline at various intervals after infection, and the subsequent clearance of pneumococci was determined. Viable pneumococci were rapidly killed by lung defenses if bacterial multiplication was inhibited within 12 h of the onset of infection. No change occurred in the bacterial population if tetracycline was delayed until 24 h after infection, indicating that pneumococcal killing by lung defenses had ceased. This effect could be reproduced with the addition of pneumococcal capsular polysaccharide to the inoculum, which produced a dose-related inhibition of pneumococcal clearance. The clearance of Staphylococcus epidermidis was not impaired in the presence of pneumococcal pneumonia or by administration of exogenous capsular polysaccharide. Pneumococcal pneumonia apparently causes a marked impairment in lung antipneumococcal defenses within 24 h of the onset of infection. This acquired defect in antibacterial defenses may be due to the accumulation of pneumococcal capsular material in the lungs of infected animals.