Anaerobes may develop soft tissue infection sites after a brief passage through air, or through a more oxidizing environment than they encounter in their normal habitat. Although little information concerning the sundry effects of oxygen, antioxidant enzymes such as superoxide dismutase and catalase, and nutrient sources upon the ability of aerobes or aerotolerant species to generate a soft tissue infection, that information is virtually nonexistant for anaerobes. The purpose of the proposed research is to determine the effects of intracellular and intercellular levels of superoxide dismutase and catalase upon the ability of Bacteroides fragilis and other anaerobes to resist oxygen dependent phagocytic cell destruction, develop an experimental infection site, and withstand hyperbaric oxygen and oxygen metabolite stress. B. fragilis contains an O2-inducible superoxide dismutase. Increased levels of that enzyme impart resistance to hyperbaric oxygen stress. The susceptibility of induced and uninduced cells to phagocytic kill and their ability to generate an abscess in situ will be correlated. Catalase levels may be manipulated by varying both glucose and hemin levels during culture of B. fragilis. Cells with altered catalase levels will also be subjected to the test systems described herein. These studies are designed to seek quantitative answers to questions concerning aerotolerance and the infection process.