TAXONOMY: Bacteria -> Bacteroidetes/Chlorobi group -> Bacteroidetes -> Bacteroidia -> Bacteroidales -> Bacteroidaceae -> Bacteroides
Bacteroides is a genus of Gram-negative, obligate anaerobic bacteria. Bacteroides species are non-endospore-forming bacilli, 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 acidin 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; however, the main sources of energy for Bacteroides species in the gut are complex host-derived and plant glycans. 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.One of the most important clinically is Bacteroides fragilis.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. Although Bacteroides species are anaerobic, they are transiently 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 andtetracycline. 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.There are data suggesting that members of Bacteroides affects the lean or obese phenotype in humans. In this article, one human twin is obese while the other is lean. Their fecal microbiota is transplanted into germ-free mouse and, interestingly, the phenotype in mouse-model corresponds to that in human. Bacteroides play a key role in helping us digest the vegetable and whole-grain components of a lean, low-fat diet. As they don't break down fats well, Bacteroides are found more in people following low-fat diets. These bugs also break complex sugars down into simpler more digestible ones - possibly to the detriment of diabetics, who seem to harbor more of these bugs than does the general populace. A lower ratio of Bacteroides to Prevotella is reputed to identify the type 2 'enterotype.' [PMC 3728647] Nonalcoholic fatty liver disease (NAFLD) severity associates with gut dysbiosis and a shift in metabolic function of the gut microbiota. One study identified Bacteroides as independently associated with NASH and Ruminococcus with significant fibrosis. [PMID: 26600078 ] Clindamycin treatment affected gut Bacteroides up to two years following cessation of treatment. Similarly, three individuals with dyspepsia given one week of metronidazole, clarithromycin, and omeprazole had a state shift that persisted up to four years without additional antibiotic treatment. [PMC 3577372]
A study on mice with gut inflammation fed yeast-derived beta-glucans (BGs) demonstrated a shift in the abundance of gut microbiota towards Bacteroides (by 16%; P = 0.049) and Verrucomicrobia (mean ± SD: control = 7.8 ± 0.44 vs. YBG = 21.0 ± 9.6%) and a reduction in Firmicutes (by 66%; P < 0.001). The YBG group also showed significantly higher concentrations of fecal SCFAs such as acetic (by 37%; P = 0.016), propionic (by 47%; P = 0.026), and butyric (by 57%; P = 0.013) acids. Studies using B6 mice show that dietary BGs are beneficial for promoting intestinal health when the gut microbiota is intact. However, these CDPs may produce adverse effects if gut microbiota is compromised. [PMID: 31879786].
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]