Aerobic and Anaerobic Bacterial Interactions in the Development of Anaerobic Bacterial Pneumonia

Abstract

The interactions between aerobic and anaerobic bacteria in the development of anaerobic bacterial pneumonia were studied by introducing Bacteroides fragilis and Escherichia coli alone or in combination into guinea pigs by tracheal infusion. The lung lesions induced by B. fragilis were mainly located near the pleura, unlike those induced by E. coli, and were accompanied by pneumonia, lung abscess. and uleuritis. The lung lesions produced by mixed infection with B. fragilis (10⁹ cfu) and E. coli (10⁷ cfu) were significantly more severe than those induced by either microbe alone, and the redox potentials at the foci of inflammation were markedly reduced (max: 330 mV). Analysis of lung lesions after treatment with aztreonam and clindamycin and neutrophil phagocytic activity suggested that E. coli was primarily responsible for the lung lesions and that B. fragilis promoted the accompanying inflammation, resulting in increased pathogenicity of the mixed infections.