Bacteroides

Bacteroides
Bacteroides spp. anaerobically cultured in blood agar medium.
Scientific classification
Kingdom:	Bacteria
Phylum:	Bacteroidetes
Class:	Bacteroidetes
Order:	Bacteroidales
Family:	Bacteroidaceae
Genus:	Bacteroides Castellani & Chalmers 1919
Species
B. acidifaciens B. distasonis (reclassified as Parabacteroides distasonis) B. gracilis B. fragilis B. oris B. ovatus B. putredinis B. pyogenes B. stercoris B. suis B. tectus B. thetaiotaomicron B. vulgatus etc.

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.^[1] 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,^[2] where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine.^[3][4][5] As many as 10¹⁰-10¹¹ cells per gram of human feces have been reported.^[6] 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 ^[7].

One of the most important clinically is Bacteroides fragilis.

Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia.^[8]

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.^[9] 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.^{[10] [11]}

Microbiological Applications

An alternative fecal indicator organism, Bacteroides, has been suggested because they make up a significant portion of the fecal bacterial population,^[1] have a high degree of host specificity that reflects differences in the digestive system of the host animal,^[12] and have a small potential to grow in the environment.^[13] 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.^[14] 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 (0-4C)^[15]

See also

• Flavobacterium
• Cytophaga

References

External links

• Bacteroides infections in E Medicine
• Bacteroides in detail.