''Bacteroides'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
Gram-negative
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
,
obligate anaerobic
Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environme ...
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
. ''Bacteroides'' species are non
endospore
An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., no ...
-forming
bacilli
Bacilli is a taxonomic class of bacteria that includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens such as ''Bacillus anthracis'' (the cause of anthrax). ''Bacilli'' are almost exclusively gram-positive ...
, and may be either
motile
Motility is the ability of an organism to move independently, using metabolic energy.
Definitions
Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...
or nonmotile, depending on the species.
The DNA base composition is 40–48%
GC. Unusual in bacterial organisms, ''Bacteroides'' membranes contain
sphingolipid
Sphingolipids are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extracts in the 1870s and were named after the mythological sphinx because ...
s. They also contain
meso-diaminopimelic acid
Diaminopimelic acid (DAP) is an amino acid, representing an epsilon-carboxy derivative of lysine.
DAP is a characteristic of certain cell walls of some bacteria. DAP is often found in the peptide linkages of NAM-NAG chains that make up the cell ...
in their
peptidoglycan layer
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ba ...
.
''Bacteroides'' species are normally
mutualistic, making up the most substantial portion of the mammalian
gastrointestinal microbiota,
where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine.
As many as 10
10–10
11 cells per gram of human feces have been reported. They can use
simple sugars
Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built.
They are usually colorless, water-solub ...
when available; however, the main sources of energy for ''Bacteroides'' species in the gut are complex host-derived and plant
glycan
The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may also be used to refer to the carbohydrate p ...
s.
Studies indicate that long-term diet is strongly associated with the
gut microbiome
Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mic ...
composition—those who eat plenty of protein and animal fats have predominantly ''Bacteroides'' bacteria, while for those who consume more carbohydrates the ''
Prevotella
''Prevotella'' is a genus of Gram-negative bacteria.
''Prevotella'' spp. are members of the oral, vaginal, and gut microbiota and are often recovered from anaerobic infections of the respiratory tract. These infections include aspiration pneum ...
'' species dominate.
One of the most important clinically is ''
Bacteroides fragilis
''Bacteroides fragilis'' is an anaerobic, Gram-negative, pleomorphic to rod-shaped bacterium. It is part of the normal microbiota of the human colon and is generally commensal, but can cause infection if displaced into the bloodstream or surroun ...
''.
''
Bacteroides melaninogenicus
''Prevotella melaninogenica'' is a species of bacterium in the normal microbiota of the upper respiratory tract. It is an important human pathogen in various anaerobic infections, often mixed with other aerobic and anaerobic bacteria. ''P. melan ...
'' has recently been reclassified and split into ''
Prevotella melaninogenica
''Prevotella melaninogenica'' is a species of bacterium in the normal microbiota of the upper respiratory tract. It is an important human pathogen in various anaerobic infections, often mixed with other aerobic and anaerobic bacteria. ''P. melan ...
'' and ''
Prevotella intermedia
''Prevotella intermedia'' (formerly ''Bacteroides intermedius'') is a gram-negative, obligate anaerobic pathogenic bacterium involved in periodontal infections, including gingivitis and periodontitis, and often found in acute necrotizing ulcerat ...
''.
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
Appendicitis is inflammation of the appendix. Symptoms commonly include right lower abdominal pain, nausea, vomiting, and decreased appetite. However, approximately 40% of people do not have these typical symptoms. Severe complications of a rup ...
via abscess formation, inhibiting
phagocytosis
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...
, and inactivating
beta-lactam antibiotics
β-lactam antibiotics (beta-lactam antibiotics) are antibiotics that contain a beta-lactam ring in their chemical
structure. This includes penicillin derivatives (penams), cephalosporins and cephamycins (cephems), monobactams, carbapenems and ...
.
Although ''Bacteroides'' species are anaerobic, they are transiently
aerotolerant
Aerotolerant anaerobes use fermentation to produce ATP. They do not use oxygen, but they can protect themselves from reactive oxygen molecules. In contrast, obligate anaerobes can be harmed by reactive oxygen molecules.
There are three categorie ...
and thus can survive in the abdominal cavity.
In general, ''Bacteroides'' are resistant to a wide variety of
antibiotic
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...
s—β-lactams,
aminoglycosides
Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside ( sugar). The term can also refer ...
, and recently many species have acquired resistance to
erythromycin
Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used duri ...
and
tetracycline
Tetracycline, sold under various brand names, is an oral antibiotic in the tetracyclines family of medications, used to treat a number of infections, including Acne vulgaris, acne, cholera, brucellosis, plague (disease), plague, malaria, and sy ...
. This high level of
antibiotic resistance
Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
has prompted concerns that ''Bacteroides'' species may become a reservoir for resistance in other, more highly pathogenic bacterial strains.
It has been often considered susceptible to
clindamycin
Clindamycin is an antibiotic medication used for the treatment of a number of bacterial infections, including osteomyelitis (bone) or joint infections, pelvic inflammatory disease, strep throat, pneumonia, acute otitis media (middle ear infec ...
,
but recent evidence demonstrated an increasing trend in clindamycin resistance rates (up to 33%).
Microbiological applications
An alternative fecal indicator organism, ''Bacteroides'', has been suggested because they make up a significant portion of the fecal bacterial population,
have a high degree of host specificity that reflects differences in the digestive system of the host animal 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 A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be ...
. 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).
Early research suggests tha
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."
Another study showed a 5.6-times higher risk of osteoporosis fractures in the low Bacteroides group of Japanese postmenopausal women.
Human
Members of the
Bacillota
The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom continue to use the earl ...
and
Bacteroidota
The phylum Bacteroidota (synonym Bacteroidetes) is composed of three large classes of Gram-negative, nonsporeforming, anaerobic or aerobic, and rod-shaped bacteria that are widely distributed in the environment, including in soil, sediments, and ...
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 to
Bacillota
The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom continue to use the earl ...
and
Actinomycetota
The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...
.
''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
''Bacteroides thetaiotaomicron'' (formerly ''Bacillus thetaiotaomicron'') is a species of bacterium of the genus ''Bacteroides''. It is a gram-negative obligate anaerobe. It is one of the most common bacteria found in human gut microbiota and is ...
''
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.
There is data suggesting that members of ''Bacteroides'' affect the lean or obese phenotype in humans.
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.
See also
* ''
CrAssphage CrAss-like phage are a bacteriophage (virus that infects bacteria) family that was discovered in 2014 by cross assembling reads in human fecal metagenomes. In silico comparative genomics and taxonomic analysis have found that crAss-like phages repre ...
''
* ''
Cytophaga
''Cytophaga'' is a genus of Gram-negative, gliding, rod-shaped bacteria. This bacterium is commonly found in soil, rapidly digests crystalline cellulose ''C. hutchinsonii'' is able to use its gliding motility to move quickly over surfaces. Al ...
''
* ''
Flavobacterium
''Flavobacterium'' is a genus of Gram-negative, nonmotile and motile, rod-shaped bacteria that consists of 130 recognized species. Flavobacteria are found in soil and fresh water in a variety of environments. Several species are known to cause ...
''
References
External links
Bacteroides infections in E Medicinein detail.
{{Taxonbar, from=Q133186
Bacteroidia
Gram-negative bacteria
Medically important anaerobes
Gut flora bacteria
Bacteria genera