Bacteroides fragilis
| Bacteroides fragilis | |
|---|---|
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| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Bacteroidetes |
| Class: | Bacteroidetes |
| Order: | Bacteroidales |
| Family: | Bacteroidaceae |
| Genus: | Bacteroides |
| Species: | Bacteroides fragilis |
| Bacteroides fragilis | |
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| Classification and external resources | |
| MeSH | D001442 |
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, but can cause infection if displaced into the bloodstream or surrounding tissue following surgery, disease, or trauma.
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.
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