The virulence of Clostridium species depends on the production of various exotoxins. These toxins are so potent that life-threatening disease can result from mild or even inapparent local tetanus infection. C. perfringens produces toxins that may cause massive tissue necrosis in startlingly short periods. In addition to promoting the replication of anaerobes, a reduced environment impairs host defense mechanisms. Anaerobiasis impairs the bactericidal activity of polymorphonuclear leukocytes, probably by preventing the oxidative burst normally responsible for oxidant-mediated bactericidal activity.
Hypoxia also impairs lymphocyte proliferation.
Finally, most antibiotics are less active at reduced oxygen tensions. Despite the heterogeneity of anaerobes, there are several properties that characterize anaerobic infections. Unlike many other infectious processes in which a single bacterial species causes one illness, anaerobic infections frequently involve multiple bacterial species. In some infections, aerobic or facultative organisms are present together with anaerobes. Because anaerobes often require specialized antimicrobial chemotherapy, it is important that the microbiology laboratory not overlook them after identification of more easily cultured aerobic species.