The exact role the anaerobic enteric flora plays in the pathogenesis and persistence of intraabdominal infections due to perforation of a hollow viscus is still unclear. Four lines of evidence have been evaluated. (1) Careful cultures of intraabdominal infections almost always yield anaerobic bacteria, but only relatively few species are predictably found, compared with the hundreds of species populating the colon. (2) Experimental models have demonstrated that the pathogenetic roles of aerobes and anaerobes differ from one another during the establishment of mixed intraabdominal sepsis. Facultative organisms induce more systemic toxicity, and anaerobes predispose to abscess formation. Evidence is inconclusive whether true synergy between aerobes and anaerobes exists in such models. (3) Studies of oral prophylactic antibiotics strongly support the important role of the anaerobic component of colonic contents in the pathogenesis of postoperative infections. (4) Studies using therapeutic antibiotics generally favor coverage for both aerobic and anaerobic components of the contaminating enteric contents. Properly performed clinical studies directed at this latter point, however, are disappointingly few.
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