Interactions between aerobic and anaerobic bacteria.

Many human infections are caused by a mixture of aerobic and anaerobic bacteria, acting in a synergistic manner. In an animal model of intraabdominal sepsis, the coliforms were responsible for acute peritonitis, septicemia, and shock, while the anaerobes, particularly Bacteroides fragilis, caused the late complications of abscess formation. Clinical trials of antimicrobial agents in patients with mixed infections have affirmed the importance of the two microbial components. Effective drug regimens provide activity against both aerobic and anaerobic pathogens.