Bacteroides

Bacteroides is a genus of Gram-negative, obligate anaerobic bacteria. Bacteroides species are non endospore-forming bacilli, and may be either motile or nonmotile, depending on the species.[3] 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
Bacteroides biacutis anaerobically cultured in blood agar medium
Scientific classification
Domain: Bacteria
Phylum: Bacteroidetes
Class: Bacteroidia
Order: Bacteroidales
Family: Bacteroidaceae
Genus: Bacteroides
Castellani & Chalmers 1919[1]
Species

Bacteroides species are normally mutualistic, making up the most substantial portion of the mammalian gastrointestinal microbiota,[4] where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine.[5][6][7] As many as 1010–1011 cells per gram of human feces have been reported.[8] 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.[9] 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.[10]

One of the most important clinically is Bacteroides fragilis.

Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia.[11]

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.[12] Although Bacteroides species are anaerobic, they are transiently aerotolerant[13] 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.[14][15] It is susceptible to clindamycin.[16]

Microbiological applications

An alternative fecal indicator organism, Bacteroides, has been suggested because they make up a significant portion of the fecal bacterial population,[3] have a high degree of host specificity that reflects differences in the digestive system of the host animal[17] 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.[18] This technique allows quantification of genetic markers that are specific to the host of the bacteria Bacteroides and 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).[19]

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."[20]

Human

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 such as Bacteroides thetaiotaomicron[21] 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.[22]

There is data suggesting that members of Bacteroides affect the lean or obese phenotype in humans.[23] In this article, one human twin is obese while the other is lean. When their fecal microbiota is transplanted into germ-free mice, the phenotype in the mouse model corresponds to that in humans.

References
  1. Castellani, A., and Chalmers, A.J. Manual of Tropical Medicine, 3rd ed. (1919). Williams Wood and Co., New York.
  2. Parte, A.C. "Bacteroides". www.bacterio.net.
  3. Madigan M, Martinko J, eds. (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 978-0-13-144329-7.
  4. Dorland WAN (editor) (2003). Dorland's Illustrated Medical Dictionary (30th ed.). W.B. Saunders. ISBN 978-0-7216-0146-5.CS1 maint: extra text: authors list (link)
  5. Wexler HM (October 2007). "Bacteroides: the good, the bad, and the nitty-gritty". Clinical Microbiology Reviews. 20 (4): 593–621. doi:10.1128/CMR.00008-07. PMC 2176045. PMID 17934076.
  6. Xu J, Gordon JI (September 2003). "Honor thy symbionts". Proceedings of the National Academy of Sciences of the United States of America. 100 (18): 10452–9. Bibcode:2003PNAS..10010452X. doi:10.1073/pnas.1734063100. PMC 193582. PMID 12923294.
  7. Xu J, Mahowald MA, Ley RE, Lozupone CA, Hamady M, Martens EC, Henrissat B, Coutinho PM, Minx P, Latreille P, Cordum H, Van Brunt A, Kim K, Fulton RS, Fulton LA, Clifton SW, Wilson RK, Knight RD, Gordon JI (July 2007). "Evolution of symbiotic bacteria in the distal human intestine". PLoS Biology. 5 (7): e156. doi:10.1371/journal.pbio.0050156. PMC 1892571. PMID 17579514.
  8. 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 978-0-12-341280-5.
  9. Martens EC, Chiang HC, Gordon JI (November 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 2605320. PMID 18996345.
  10. 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 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 3368382. PMID 21885731.
  11. "Bacteroides Infection: Overview - eMedicine". Archived from the original on 22 December 2008. Retrieved 2008-12-11.
  12. Ryan KJ, Ray CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 978-0-8385-8529-0.
  13. Baughn, Anthony; Malamy, Michael (2004). "Molecular Basis for Aerotolerance of the Obligately Anaerobic Bacteroides Spp.". In Nakano, Michiko; Zuber, Peter (eds.). Strict and Facultative Anaerobes: Medical and Environmental Aspects. CRC Press. p. 161. ISBN 978-1-904933-03-8.
  14. Salyers AA, Gupta A, Wang Y (September 2004). "Human intestinal bacteria as reservoirs for antibiotic resistance genes". Trends in Microbiology. 12 (9): 412–6. doi:10.1016/j.tim.2004.07.004. PMID 15337162.
  15. Löfmark S, Jernberg C, Jansson JK, Edlund C (December 2006). "Clindamycin-induced enrichment and long-term persistence of resistant Bacteroides spp. and resistance genes". The Journal of Antimicrobial Chemotherapy. 58 (6): 1160–7. doi:10.1093/jac/dkl420. PMID 17046967.
  16. "Clindamycin" (PDF). Davis. 2017. Retrieved March 24, 2017.
  17. Bernhard AE, Field KG (October 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): 4571–4. doi:10.1128/AEM.66.10.4571-4574.2000. PMC 92346. PMID 11010920. Archived from the original (PDF) on 2010-07-05. Retrieved 2011-02-17.
  18. Layton A, McKay L, Williams D, Garrett V, Gentry R, Sayler G (June 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): 4214–24. doi:10.1128/AEM.01036-05. PMC 1489674. PMID 16751534.
  19. 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". Journal of Environmental Quality. 38 (3): 1224–32. doi:10.2134/jeq2008.0258. PMID 19398520.
  20. "Gut bacteria influence the brain indirectly, study shows". Medical News Today. Retrieved 2018-01-07.
  21. Wexler HM (October 2007). "Bacteroides: the good, the bad, and the nitty-gritty". Clinical Microbiology Reviews. 20 (4): 593–621. doi:10.1128/CMR.00008-07. PMC 2176045. PMID 17934076.
  22. 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.
  23. Ridaura VK, Faith JJ, Rey FE, Cheng J, Duncan AE, Kau AL, Griffin NW, Lombard V, Henrissat B, Bain JR, Muehlbauer MJ, Ilkayeva O, Semenkovich CF, Funai K, Hayashi DK, Lyle BJ, Martini MC, Ursell LK, Clemente JC, Van Treuren W, Walters WA, Knight R, Newgard CB, Heath AC, Gordon JI (September 2013). "Gut microbiota from twins discordant for obesity modulate metabolism in mice". Science. 341 (6150): 1241214. doi:10.1126/science.1241214. PMC 3829625. PMID 24009397.
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