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An infection caused by anaerobic bacteria (organisms that are intolerant of oxygen). Most such infections are mixed, involving more than one anaerobe and often aerobic or facultative bacteria as well. Anaerobes are prevalent throughout the body as indigenous flora, and virtually all anaerobic infections arise endogenously, the principal exception being Clostridium difficile colitis. Factors predisposing to anaerobic infection include those disrupting mucosal or other surfaces (trauma, surgery, and malignancy or other disease), those lowering redox potential (impaired blood supply, tissue necrosis, and growth of nonanaerobic bacteria), drugs inactive against anaerobes (such as aminoglycosides), and virulence factors produced by the anaerobes (toxins, capsules, and collagenase, hyaluronidase, and other enzymes). Anaerobic gram-negative bacilli (Bacteroides, Prevotella, Porphyromonas, Fusobacterium) and anaerobic gram-positive cocci (Peptostreptococcus) are the most common anaerobic pathogens. Clostridium (spore formers) may cause serious infection. The prime pathogen among gram-positive nonsporulating anaerobic bacilli is Actinomyces. Of the infections commonly involving anaerobes, the oral and dental pleuropulmonary, intraabdominal, obstetric-gynecologic, and skin and soft tissue infections are most important in terms of frequency of occurrence. To document anaerobic infection properly, specimens for culture must be obtained so as to exclude normal flora and must be transported under anaerobic conditions. Therapy includes surgery and antimicrobial agents. See Antibiotic, Infection
a group of severe diseases caused by pathogenic anaerobes. More often the term “anaerobic infection” is used to indicate gas gangrene. Anaerobes also cause tetanus, botulism, and other diseases.