Bacteroides species are normallymutualistic, making up the most substantial portion of the mammaliangastrointestinal 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 usesimple sugars when available; however, the main sources of energy forBacteroides species in the gut are complex host-derived and plantglycans.[9] Studies indicate that long-term diet is strongly associated with thegut microbiome composition—those who eat a higher proportion of protein and animal fats have predominantlyBacteroides bacteria, while for those who consume more carbohydrates or fiber thePrevotella species dominate.[10]
In general,Bacteroides are resistant to a wide variety ofantibiotics—β-lactams,aminoglycosides, and recently many species have acquired resistance toerythromycin andtetracycline. This high level ofantibiotic resistance has prompted concerns thatBacteroides species may become a reservoir for resistance in other, more highly pathogenic bacterial strains.[16][17] It has been often considered susceptible toclindamycin,[18] but recent evidence demonstrated an increasing trend in clindamycin resistance rates (up to 33%).[19]
In cases whereBacteroides can move outside the gut due to gastrointestinal tract rupture or intestinal surgery,Bacteroides can infect several parts of the human body.Bacteroides can enter thecentral nervous system by penetrating theblood brain barrier through theolfactory andtrigeminal cranial nerves and can causemeningitis and brain abscesses.[20]Bacteroides has also been isolated from abscesses in the neck and lungs. SomeBacteroides species are associated withCrohn's disease,appendicitis andinflammatory bowel disease.Bacteroides species play multiple roles within the human gut microbiome.[5]
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[21] 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 ofBacteroides by using qPCR to quantify the host-specific 16S rRNAgenetic marker.[22] 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).[23]
"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."[24]
Another study showed a 5.6-times higher risk of osteoporosis fractures in the low Bacteroides group of Japanese postmenopausal women.[25]
Members of theBacillota andBacteroidota phyla make up a majority of the bacterial species in the human intestinal microbiota (the "gut microbiome"). The healthy human gut microbiome consists of 109 abundant species of which 31 (19.7%) are members of the Bacteroidetes while 63 (40%) and 32 (20%) belong toBacillota andActinomycetota.[26]
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 asBacteroides thetaiotaomicron[5] 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.[27]
There is data suggesting that members ofBacteroides affect the lean or obese phenotype in humans.[28] 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.[citation needed]
Bacteroides are symbiont colonizers of their host intestinal niche and serve several physiological functions, some of which can be beneficial while others are detrimental.Bacteroides participate in the regulation of the intestinal micro-environment andcarbohydrate metabolism with the capacity to adapt to the host environment by hydrolyzingbile salts.[29] SomeBacteroides produceacetate andpropionate during sugar fermentation. Acetate can prevent the transport of toxins from the gut to the blood while propionate can prevent the formation of tumors in the human colon.[30]
Bacteroides such asBacteroides uniformis may play a role in alleviatingobesity. Low abundance ofB. uniformis found in the intestine of formula-fed infants were associated with a high risk of obesity.[31] AdministeringB. uniformis orally may alleviate metabolic and immune dysfunction which may contribute to obesity in mice. Similarly,Bacteroides acidifaciens may assist the activating fat oxidation inadipose tissue and thus could protect against obesity.[32][30]
^Finegold SM, Sutter VL, Mathisen GE (1983).Normal indigenous intestinal flora (pp. 3-31) in Human intestinal microflora in health and disease. Academic Press.ISBN978-0-12-341280-5.
^Appleman MD, Heseltine PN, Cherubin CE (Jan 1990). "Epidemiology, antimicrobial susceptibility, pathogenicity, and significance of Bacteroides fragilis group organisms isolated at Los Angeles County-University of Southern California Medical Center".Reviews of Infectious Diseases.13 (1):12–18.doi:10.1093/clinids/13.1.12.PMID2017610.
^Ryan KJ, Ray CG, eds. (2004).Sherris Medical Microbiology (4th ed.). McGraw Hill.ISBN978-0-8385-8529-0.
^Baughn A, Malamy M (2004). "Molecular Basis for Aerotolerance of the Obligately Anaerobic Bacteroides Spp.". In Nakano M, Zuber P (eds.).Strict and Facultative Anaerobes: Medical and Environmental Aspects. CRC Press. p. 161.ISBN978-1-904933-03-8.
^Salyers AA, Gupta A, Wang Y (September 2004). "Human intestinal bacteria as reservoirs for antibiotic resistance genes".Trends in Microbiology.12 (9):412–416.doi:10.1016/j.tim.2004.07.004.PMID15337162.
^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):1160–1167.doi:10.1093/jac/dkl420.PMID17046967.
^abWang C, Zhao J, Zhang H, Lee YK, Zhai Q, Chen W (2021-11-30). "Roles of intestinalbacteroides in human health and diseases".Critical Reviews in Food Science and Nutrition.61 (21):3518–3536.doi:10.1080/10408398.2020.1802695.PMID32757948.S2CID221036664.
