Anaerobic infections in the surgical patient: microbial etiology and therapy.

Anaerobic infections occur in surgical patients in part because of structural or functional defects in the host that (1) cause a breech in the normal mucosal barriers, (2) create localized vascular insufficiencies, or (3) produce an obstruction. Any or all of these events may compromise the oxidation-reduction potential within the tissues, encouraging rapid anaerobic growth. Although diverse anaerobic populations are spread throughout the gastrointestinal tract, a relatively limited number of organisms are responsible for clinical infection in the surgical patient. Many of these offending organisms express overt virulence factors that enhance microbial adherence, tissue destruction, and, in the case of Bacteroides fragilis, facilitate abscess formation. The selection of an appropriate perioperative or therapeutic agent requires a fundamental knowledge of the microbial ecology of this microbial population. The failure to consider the anaerobic flora as a component in the etiology of mixed surgical infections is associated with a high rate of perioperative and therapeutic failures.