Bacteroides species are anaerobic bacteria that are predominant components of the bacterial florae of mucous membranes and are therefore a common cause of endogenous infections. Bacteroides infections can develop in all body sites, including the CNS, the head, the neck, the chest, the abdomen, the pelvis, the skin, and the soft tissues. Inadequate therapy against these anaerobic bacteria may lead to clinical failure.
Because of their fastidiousness, they are difficult to isolate and are often overlooked. Their isolation requires appropriate methods of collection, transportation, and cultivation of specimens. Treatment is complicated by 3 factors: slow growth, increasing resistance to antimicrobial agents, and the polymicrobial synergistic nature of the infection.
The B fragilis group, a member of the Bacteroidaceae family, includes B fragilis (causes the most clinical infections), Bacteroides distasonis, Bacteroides ovatus, Bacteroides thetaiotaomicron, and Bacteroides vulgatus. These bacteria are resistant to penicillins, mostly through the production of beta-lactamase. They are part of the normal GI florae and predominate in intra-abdominal infections and infections that originate from those florae (eg, perirectal abscesses, decubitus ulcers). Enterotoxigenic B fragilis (ETBF) is also a potential cause of diarrhea.
Pigmented Prevotella, such as Prevotella melaninogenica and Prevotella intermedia (which were previously called the Bacteroides melaninogenicus group), Porphyromonas (eg, Porphyromonas asaccharolytica), and nonpigmented Prevotella (eg, Prevotella oralis, Prevotella oris) are part of the normal oral and vaginal florae and are the predominant AGNB isolated from respiratory tract infections and their complications, including aspiration pneumonia, lung abscess, chronic otitis media, chronic sinusitis, abscesses around the oral cavity, human bites, paronychia, brain abscesses, and osteomyelitis. Prevotella bivia and Prevotella disiens (previously called Bacteroides) are important in obstetric and gynecologic infections
REF: http://emedicine.medscape.com/article/233339-overview Access: 13,apr,2011
Author: Itzhak Brook, MD, MSc; Chief Editor: Burke A Cunha, MD
Bacteroides is a genus of Gram-negative, bacillus bacteria. Bacteroides species are non-endospore-forming, anaerobes, and may be either motile or non-motile, depending on the species. 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 mutualistic, making up the most substantial portion of the mammalian gastrointestinal flora, 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. They can use simple sugars when available, but the main source of energy is polysaccharides from plant sources.
One of the most important clinically is Bacteroides fragilis.
Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia.
PathogenesisBacteroides 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. Although Bacteroides species are anaerobic, they are aerotolerant and thus can survive in the abdominal cavity.
In general, Bacteroides are resistant to a wide variety of antibiotics — β-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. 
Microbiological ApplicationsAn alternative fecal indicator organism, Bacteroides, has been suggested because they make up a significant portion of the fecal bacterial population, have a high degree of host specificity that reflects differences in the digestive system of the host animal, and have a small potential to grow in the environment. Over the past decade, real-time polymerase chain reaction (PCR) methods have been utilized to detect the presence of various microbial pathogens through the amplification of specific DNA sequences without culturing bacteria. One study has measured the amount of Bacteroides by using qPCR to quantify the 16S rRNA genetic marker that is host-specific. This technique allows quantification of genetic markers that are specific to the host of the bacteria and allow detection of recent contamination. A recent report found that temperature plays a major role in the amount of time the bacteria will persist in the environment, the life span increases with colder temperatures
References1.^ Madigan M, Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1.
2.^ Dorland WAN (editor) (2003). Dorland's Illustrated Medical Dictionary (30th ed.). W.B. Saunders. ISBN 0-7216-0146-4.
3.^ Wexler, H. M. (Oct 2007). "Bacteroides: the good, the bad, and the nitty-gritty" (Free full text). Clinical microbiology reviews 20 (4): 593–621. doi:10.1128/CMR.00008-07. ISSN 0893-8512. PMC 2176045. PMID 17934076. http://cmr.asm.org/cgi/pmidlookup?view=long&pmid=17934076. edit
4.^ Xu, J.; Gordon, I. (Sep 2003). "Inaugural Article: Honor thy symbionts" (Free full text). Proceedings of the National Academy of Sciences of the United States of America 100 (18): 10452–10459. doi:10.1073/pnas.1734063100. ISSN 0027-8424. PMC 193582. PMID 12923294. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=12923294. edit
5.^ Xu, J.; Mahowald, A.; Ley, E.; Lozupone, A.; Hamady, M.; Martens, C.; Henrissat, B.; Coutinho, M. et al. (Jul 2007). "Evolution of symbiotic bacteria in the distal human intestine" (Free full text). PLoS biology 5 (7): e156. doi:10.1371/journal.pbio.0050156. ISSN 1544-9173. PMC 1892571. PMID 17579514. http://dx.plos.org/10.1371/journal.pbio.0050156. edit
6.^ 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.
7.^ "Bacteroides Infection: Overview - eMedicine". http://emedicine.medscape.com/article/233339-overview. Retrieved 2008-12-11.
8.^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
9.^ Salyers AA, Gupta A, Wang Y (2004). "Human intestinal bacteria as reservoirs for antibiotic resistance genes". Trends Microbiol 12 (9): 412–6. doi:10.1016/j.tim.2004.07.004. PMID 15337162.
10.^ Löfmark, S.; Jernberg, C.; Jansson, K.; Edlund, C. (Dec 2006). "Clindamycin-induced enrichment and long-term persistence of resistant Bacteroides spp. And resistance genes" (Free full text). The Journal of antimicrobial chemotherapy 58 (6): 1160–1167. doi:10.1093/jac/dkl420. ISSN 0305-7453. PMID 17046967. http://jac.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=17046967. edit
11.^ Madigan M, Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1.
12.^ Bernhard and Field, A.E. and K.G.; Field, KG (2000). "A PCR Assay To Discriminate Human and Ruminant Feces on the Basis of Host Differences in Bacteroides-Prevotella Genes Encoding 16S rRNA". Applied and Environmental Microbiology 66 (10): 4571–4574. doi:http://water.rutgers.edu/Source_Tracking/Bacteroidetes/APCRAssayToDiscriminateHumanandRuminantFecesontheBasisofHostDifferencesinBacteroides.pdf. PMC 92346. PMID 11010920. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=92346.
13.^ Kreader, C.A. (1998). "Persistence of PCR-Detectable Bacteroides distasonis from Human Feces in River Water". Applied and Environmental Microbiology 64 (10): 4103–4105. doi:http://www.water.rutgers.edu/Source_Tracking/Bacteroidetes/PersistenceofPCR-DetectableBacteroidesdistasonisfromHumanFecesinRiverWater.pdf. PMC 106613. PMID 9758854. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=106613.
14.^ Layton, A.; McKay, L; Williams, D; Garrett, V; Gentry, R; Sayler, G (2006). "Development of Bacteroides 16S rRNA Gene TaqMan-Based Real-Time PCR Assays for Estimation of Total, Human,and Bovine Fecal Pollution in Water". Applied and Environmental Microbiology 72 (6): 4214–4224. doi:http://aem.asm.org/cgi/content/short/72/6/4214. PMC 1489674. PMID 16751534. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1489674.
15.^ Bell, Layton, McKay, Williams, Gentry, Sayler, A., A.C., L., D., R., G.S.; Layton, Alice C.; McKay, Larry; Williams, Dan; Gentry, Randy; Sayler, Gary S. (2009). "Factors Influencing the Persistance of Fecal Bacteroides in Stream Water". J. Environ. Qual. 38 (3): 1224–1232. doi:10.2134/jeq2008.0258. PMID 19398520.
REF: http://en.wikipedia.org/wiki/Bacteroides .Access: 13/apr/2011