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Overview of Anaerobic Bacteria
Bacteria can be classified by their need and tolerance for O 2 :
Obligate anaerobes replicate at sites with low oxidation-reduction potential (eg, necrotic, devascularized tissue). Obligate anaerobes have been categorized based on their O 2 tolerance: strict anaerobes grow in ≤ 0.4% O 2 ; moderate anaerobes grow in 0.8 to 2.5% O 2 ; and aerotolerant anaerobes grow in ≥ 2.5% O 2 . The obligate anaerobes that commonly cause infection can tolerate atmospheric O 2 for at least 8 h and frequently for up to 72 h.
Obligate anaerobes are major components of the normal microflora on mucous membranes, especially of the mouth, lower GI tract, and vagina; these anaerobes cause disease when normal mucosal barriers break down.
Gram-negative anaerobes and some of the infections they cause include
Gram-positive anaerobes and some of the infections they cause include
Actinomyces: Head, neck, abdominal, and pelvic infections and aspiration pneumonia
Clostridium: Gas gangrene due to C. perfringens, food poisoning due to C. perfringens type A, botulism due to C. botulinum, tetanus due to C. tetani, and C. difficile–induced diarrhea (pseudomembranous colitis)
Peptostreptococcus: Oral, respiratory, and intra-abdominal infections
Propionibacterium: Foreign body infections (eg, in a cerebrospinal fluid shunt, prosthetic joint, or cardiac device)
Anaerobic infections are typically suppurative, causing abscess formation and tissue necrosis (often the result of thrombophlebitis, gas formation, or both). Many anaerobes produce tissue-destructive enzymes as well as some of the most potent paralytic toxins known.
Clues to anaerobic infection include
Specimens for anaerobic culture should be obtained by aspiration or biopsy from normally sterile sites. Delivery to the laboratory should be prompt, and transport devices should provide an O 2 -free atmosphere of carbon dioxide, hydrogen, and nitrogen. Swabs are best transported in an anaerobically sterilized, semisolid medium such as Cary-Blair transport medium.
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