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''Bacteroides fragilis'' is an obligately anaerobic, Gram-negative, rod-shaped bacterium. It is part of the normal flora of the human colon and is generally commensal,〔http://prod.hopkins-abxguide.org/pathogens/bacteria/anaerobic_gram-neg._bacilli/bacteroides_fragilis.html?contentInstanceId=255919〕 but can cause infection if displaced into the bloodstream or surrounding tissue following surgery, disease, or trauma. ==Epidemiology and pathogenesis== The ''B. fragilis'' group is the most commonly isolated Bacteroidaceae in anaerobic infections, especially those that originate from the gastrointestinal flora. ''B. fragilis'' is the most prevalent organism in the ''B. fragilis'' group, accounting for 41% to 78% of the isolates of the group. These organisms are resistant to penicillin by virtue of production of beta-lactamase, and by other unknown factors. This group was formerly classified as subspecies of ''B. fragilis'' (i.e. ''B. f.'' ssp. ''fragilis'', ''B. f.'' ssp. ''distasonis'', ''B. f.'' ssp. ''ovatus'', ''B. f.'' ssp. ''thetaiotaomicron'', and ''B. f.'' ssp. ''vulgatus''). They have been reclassified into distinct species on the basis of DNA homology studies. ''B. fragilis'' (formerly known as ''B. f.'' ssp. ''fragilis'') is often recovered from blood, pleural fluid, peritoneal fluid, wounds, and brain abscesses. Although the ''B. fragilis'' group is the most common species found in clinical specimens, it is the least common ''Bacteroides'' present in fecal flora, comprising only 0.5% of the bacteria present in stool. Their pathogenicity partly results from their ability to produce capsular polysaccharide, which is protective against phagocytosis and stimulates abscess formation. ''B. fragilis'' is involved in 90% of anaerobic peritoneal infections. It also causes bacteremia associated with intraabdominal infections, peritonitis and abscesses following rupture of viscus, and subcutaneous abscesses or burns near the anus.Though it is gram negative, it has an altered LPS and does not cause endotoxic shock. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bacteroides fragilis」の詳細全文を読む スポンサード リンク
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