Bacteroides

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iBacteroides

Bacteroides spp. anaerobically cultured in blood agar medium.

Scientific classification

Kingdom:	Bacteria
Phylum:	Bacteroidetes
Order:	Bacteroidales
Family:	Bacteroidaceae
Genus:	Bacteroides Castellani & Chalmers 1919

Species

B. acidifaciens
B. distasonis
B. gracilis
B. fragilis
B. oris
B. ovatus
B. putredinis
B. pyogenes
B. stercoris
B. suis
B. tectus
B. thetaiotaomicron
B. vulgatus
etc.

Bacteroides is a genus of Gram-negative, rod-shaped bacteria. Bacteroides species are non-endospore-forming, anaerobes, and may either be motile or non-motile, depending on the species.<ref>Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms, 11th ed., Prentice Hall. ISBN 0-13-144329-1.</ref> The DNA base composition is 40-48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids. They also contain meso-diaminopimelic acid in their peptidoglycan layer.

Bacteroides are normally commensal, making up the most substantial portion of the mammalian gastrointestinal flora<ref name=Dorland>Dorland WAN (editor) (2003). Dorland's Illustrated Medical Dictionary, 30th, W.B. Saunders. ISBN 0-7216-0146-4.</ref>, where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine. As many as 10¹⁰-10¹¹ cells per gram of human feces have been reported.<ref>Finegold SM; Sutter VL; Mathisen GE. (1983). Normal indigenous intestinal flora (pp. 3-31) in Human intestinal microflora in health and disease.. Academic Press. ISBN 0-12-341280-3.</ref> They can use simple sugars when available, but the main source of energy is polysaccharides from plant sources.

1 Pathogenesis
2 B. fragilis
3 References
4 See also
5 External links

[edit] Pathogenesis

Bacteroides species also benefit their host by excluding potential pathogens from colonizing the gut. Some species (B. fragilis, for example) are opportunistic human pathogens, causing infections of the peritoneal cavity, gastrointestinal surgery, and appendicitis via abscess formation, inhibiting phagocytosis, and inactivating beta-lactam antibiotics.<ref name=Sherris>Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9.</ref> Although Bacteroides species are anaerobic, they are aerotolerant and thus can survive in the abdominal cavity.

Bacteroides are generally resistant to a wide variety of antibiotics—beta-lactams, aminoglycosides, and recently many species have acquired resistance to erythromycin and tetracycline. This high level of antibiotic resistance has prompted concerns that Bacteroides species may become a reservoir for resistance in other, more highly pathogenic bacterial strains.<ref name=Salyers_2004>Salyers AA, Gupta A, Wang Y (2004). "Human intestinal bacteria as reservoirs for antibiotic resistance genes". Trends Microbiol 12 (9): 412-6. PubMed.</ref>

[edit] B. fragilis

Bacteroides fragilis is a facultative anaerobe of the gut. It is involved in, if not primarily responsible for, 90% of anaerobic peritoneal infections.^{[citation needed]} It is resistent to a wide range of antimicrobials, but susceptible to clindamycin.