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Bacteroides biacutis 01.jpg
Bacteroides spp. anaerobically cultured in blood agar medium
Scientific classification
Kingdom: Bacteria
Phylum: Bacteroidetes
Class: Bacteroidia
Order: Bacteroidales
Family: Bacteroidaceae
Genus: Bacteroides
Castellani & Chalmers 1919

Bacteroides is a genus of Gram-negative, obligate anaerobic bacteria. Bacteroides species are nonendospore-forming bacilli, and may be either motile or nonmotile, depending on the species.[2] 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 species are normally mutualistic, making up the most substantial portion of the mammalian gastrointestinal flora,[3] where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine.[4][5][6] As many as 1010–1011 cells per gram of human feces have been reported.[7] They can use simple sugars when available; however, the main sources of energy for Bacteroides species in the gut are complex host-derived and plant glycans.[8] Studies indicate that long-term diet is strongly associated with the gut microbiome composition—those who eat plenty of protein and animal fats have predominantly Bacteroides bacteria, while for those who consume more carbohydrates the Prevotella species dominate.[9]

One of the most important clinically is Bacteroides fragilis.

Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia.[10]


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.[11] Although Bacteroides species are anaerobic, they are transiently aerotolerant[12] 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.[13][14] It is susceptible to clindamycin.[15]

Microbiological applications[edit]

An alternative fecal indicator organism, Bacteroides, has been suggested because they make up a significant portion of the fecal bacterial population,[2] have a high degree of host specificity that reflects differences in the digestive system of the host animal[16] Over the past decade, real-time polymerase chain reaction (PCR) methods have been used 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 host-specific 16S rRNA genetic marker.[17] This technique allows quantification of genetic markers that are specific to the host of the bacteria a Bacteroides nd allow detection of recent contamination. A recent report found temperature plays a major role in the amount of time the bacteria will persist in the environment, the life span increases with colder temperatures (0–4 °C).[18]

Early research suggests that affects brain development.

"A new study has found that there is a three-way relationship between a type of gut bacteria, cortisol, and brain metabolites. This relationship, the researchers hypothesize, may potentially lead to further insight into autism, but more in-depth studies are needed." [19]


Bacteroides species' main source of energy is fermentation of a wide range of sugar derivatives from plant material. These compounds are common in the human colon and are potentially toxic. Bacteroides converts these sugars to fermentation products which are beneficial to humans. Bacteroides also have the ability to remove side chains from bile acids, thus returning bile acids to the hepatic circulation.[20]

There is data suggesting that members of Bacteroides affects the lean or obese phenotype in humans.[21] In this article, one human twin is obese while the other is lean. Their fecal microbiota is transplanted into germ-free mouse, and the phenotype in mouse-model corresponds to that in human. Although breast-fed infants do not show appreciable numbers in their stool until after they are weaned, Bacteroides spp. are part of normal, healthy placental microbiome.[22][23]

See also[edit]


  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq Parte, A.C. "Bacteroides". 
  2. ^ a b Madigan M, Martinko J, eds. (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1. 
  3. ^ Dorland WAN (editor) (2003). Dorland's Illustrated Medical Dictionary (30th ed.). W.B. Saunders. ISBN 0-7216-0146-4. 
  4. ^ 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 2176045Freely accessible. PMID 17934076. 
  5. ^ 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. Bibcode:2003PNAS..10010452X. doi:10.1073/pnas.1734063100. ISSN 0027-8424. PMC 193582Freely accessible. PMID 12923294. 
  6. ^ Xu, J.; Mahowald, A.; Ley, E.; Lozupone, A.; Hamady, M.; Martens, C.; Henrissat, B.; Coutinho, M.; Minx, P.; Latreille, P.; Cordum, H.; Van Brunt, A.; Kim, K.; Fulton, R. S.; Fulton, L. A.; Clifton, S. W.; Wilson, R. K.; Knight, R. D.; Gordon, J. I. (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 1892571Freely accessible. PMID 17579514. 
  7. ^ 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. 
  8. ^ Martens EC, Chiang HC, Gordon JI (2008). "Mucosal Glycan Foraging Enhances Fitness and Transmission of a Saccharolytic Human Gut Bacterial Symbiont". Cell Host Microbe. 4 (5): 447–57. doi:10.1016/j.chom.2008.09.007. PMC 2605320Freely accessible. PMID 18996345. 
  9. ^ Wu GD, Chen J, Hoffmann C, Bittinger K, Chen YY, Keilbaugh SA, Bewtra M, Knights D, Walters WA, Knight R, Sinha R, Gilroy E, Gupta K, Baldassano R, Nessel L, Li H, Bushman FD, Lewis JD (October 7, 2011). "Linking long-term dietary patterns with gut microbial enterotypes". Science. 334 (6052): 105–8. Bibcode:2011Sci...334..105W. doi:10.1126/science.1208344. PMC 3368382Freely accessible. PMID 21885731. 
  10. ^ "Bacteroides Infection: Overview - eMedicine". Archived from the original on 22 December 2008. Retrieved 2008-12-11. 
  11. ^ Ryan KJ, Ray CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9. 
  12. ^ Baughn, Anthony; Malamy, Michael (2004). "Molecular Basis for Aerotolerance of the Obligately Anaerobic Bacteroides Spp.". In Nakano, Michiko; Zuber, Peter. Strict and Facultative Anaerobes: Medical and Environmental Aspects. CRC Press. p. 161. ISBN 1-904933-03-3. 
  13. ^ Salyers AA, Gupta A, Wang Y (2004). "Human intestinal bacteria as reservoirs for antibiotic resistance genes". Trends Microbiol. 12 (9): 412–416. doi:10.1016/j.tim.2004.07.004. PMID 15337162. 
  14. ^ Löfmark, S.; Jernberg, C.; Jansson, K.; Edlund, C. (2006). "Clindamycin-induced enrichment and long-term persistence of resistant Bacteroides spp. and resistance genes". The Journal of antimicrobial chemotherapy. 58 (6): 1160–1167. doi:10.1093/jac/dkl420. PMID 17046967. 
  15. ^ "Clindamycin" (PDF). Davis. 2017. Retrieved March 24, 2017. 
  16. ^ Bernhard AE, Field KG. A PCR assay To discriminate human and ruminant feces on the basis of host differences in Bacteroides-Prevotella genes encoding 16S rRNA (Oct 2000). "A PCR assay to discriminate human and ruminant feces on the basis of host differences in Bacteroides-Prevotella genes encoding 16S rRNA" (PDF). Applied and Environmental Microbiology. 66 (10): 4571–4574. doi:10.1128/AEM.66.10.4571-4574.2000. PMC 92346Freely accessible. PMID 11010920. 
  17. ^ 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:10.1128/AEM.01036-05. PMC 1489674Freely accessible. PMID 16751534. 
  18. ^ Bell A, Layton AC, McKay L, Williams D, Gentry R, Sayler GS (27 Apr 2009). "Factors influencing the persistence of fecal Bacteroides in stream water". J Environ Qual. 38 (3): 1224–1232. doi:10.2134/jeq2008.0258. PMID 19398520. 
  19. ^ "Gut bacteria influence the brain indirectly, study shows". Medical News Today. Retrieved 2018-01-07. 
  20. ^ Slonczewski, Joan L.; Foster, John W. (2013-10-23). Microbiology: An Evolving Science (3 ed.). S.l.: W. W. Norton & Company. p. 749. ISBN 9780393123685. 
  21. ^
  22. ^ Mor, Gil; Kwon, Ja-Young (2015). "Trophoblast-microbiome interaction: a new paradigm on immune regulation". American Journal of Obstetrics and Gynecology. 213 (4): S131–S137. doi:10.1016/j.ajog.2015.06.039. ISSN 0002-9378. PMID 26428492. 
  23. ^ Todar, K. "Pathogenic E. coli". Online Textbook of Bacteriology. University of Wisconsin–Madison Department of Bacteriology. Retrieved 2007-11-30. 

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