Bifidobacterium: Difference between revisions

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{{Short description|Genus of bacteria}}

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'''''Bifidobacterium''''' is a [[genus]] of [[gram-positive]], [[Motility|nonmotile]], often branched [[Anaerobic organism|anaerobic]] [[bacteria]].  They are ubiquitous inhabitants of the [[gastrointestinal tract]] though strains have been isolated from the [[vagina]] and mouth (''[[Bifidobacterium dentium|B. dentium]]'') of mammals, including humans.  Bifidobacteria are one of the major genera of bacteria that make up the gastrointestinal tract [[microbiota]] in mammals. Some bifidobacteria are used as [[probiotic]]s.

Before the 1960s, ''Bifidobacterium'' species were collectively referred to as ''Lactobacillus bifidus''.

==History==

[[Image:20101210 013757 BifidobacteriumAnimalis.jpg|thumb|right|Some of the ''[[Bifidobacterium animalis]]'' bacteria found in a sample of Activia yogurt:&nbsp; The numbered ticks on the scale are 10 micrometres apart.]]

In 1899, [[Henri Tissier]], a French [[paediatrician|pediatrician]] at the [[Pasteur Institute]] in Paris, isolated a bacterium characterised by a Y-shaped morphology ("bifid") in the intestinal microbiota of breast-fed infants and named it "bifidus". In 1907, [[Élie Metchnikoff]], deputy director at the Pasteur Institute, propounded the theory that [[lactic acid]] bacteria are beneficial to human health. Metchnikoff observed that the [[longevity]] of Bulgarians was the result of their consumption of [[fermented milk products]]. Metchnikoff also suggested that "oral administration of cultures of fermentative bacteria would implant the beneficial bacteria in the intestinal tract".

==Metabolism==

The genus ''Bifidobacterium'' possesses a unique [[fructose-6-phosphate phosphoketolase]] pathway employed to ferment [[carbohydrate]]s.

Much metabolic research on bifidobacteria has focused on [[oligosaccharide]] metabolism, as these carbohydrates are available in their otherwise nutrient-limited habitats. Infant-associated bifidobacterial [[phylotype]]s appear to have evolved the ability to ferment [[Human milk oligosaccharide|milk oligosaccharides]], whereas adult-associated species use plant oligosaccharides, consistent with what they encounter in their respective environments. As breast-fed infants often harbor bifidobacteria-dominated gut consortia, numerous applications attempt to mimic the bifidogenic properties of milk oligosaccharides. These are broadly classified as plant-derived [[fructooligosaccharide]]s or dairy-derived [[galactooligosaccharide]]s, which are differentially metabolized and distinct from milk oligosaccharide [[catabolism]].

==Response to oxygen==

The sensitivity of members of the genus ''Bifidobacterium'' to O₂ generally limits probiotic activity to anaerobic habitats. Recent research has reported that some ''Bifidobacterium'' strains exhibit various types of [[wikt:oxic|oxic]] growth. Low concentrations of O₂ and CO₂ can have a stimulatory effect on the growth of these ''Bifidobacterium'' strains. Based on the growth profiles under different O₂ concentrations, the ''Bifidobacterium'' species were classified into four classes: O₂-hypersensitive, O₂-sensitive, O₂-tolerant, and [[microaerophilic]]. The primary factor responsible for aerobic growth inhibition is proposed to be the production of [[hydrogen peroxide]] (H₂O₂) in the growth medium. A H₂O₂-forming [[NADH]] [[oxidase]] was purified from O₂-sensitive ''Bifidobacterium bifidum'' and was identified as a ''b''-type [[dihydroorotate dehydrogenase]]. The kinetic parameters suggested that the enzyme could be involved in H₂O₂ production in highly aerated environments.

==Genomes==

Members of the genus ''Bifidobacterium'' have genome sizes ranging from 1.73 (''Bifidobacterium indicum'') to 3.25 Mb (''Bifidobacterium biavatii''), corresponding to 1,352 and 2,557 predicted protein-encoding [[open reading frame]]s, respectively.

Functional classification of ''Bifidobacterium'' genes, including the [[pan-genome]] of this genus, revealed that 13.7% of the identified bifidobacterial genes encode enzymes involved in [[carbohydrate metabolism]].

==Clinical uses==

Adding ''Bifidobacterium'' as a probiotic to conventional treatment of [[ulcerative colitis]] has been shown to be associated with improved rates of remission and improved maintenance of remission. Some ''Bifidobacterium'' strains are considered as important probiotics and used in the food industry. Different species and/or strains of bifidobacteria may exert a range of beneficial health effects, including the regulation of intestinal microbial [[homeostasis]], the inhibition of pathogens and harmful bacteria that colonize and/or infect the gut mucosa, the modulation of local and systemic immune responses, the repression of procarcinogenic enzymatic activities within the microbiota, the production of vitamins, and the bioconversion of a number of dietary compounds into bioactive molecules. Bifidobacteria improve the gut mucosal barrier and lower levels of [[lipopolysaccharide]] in the intestine.

Bifidobacteria may also improve abdominal pain in patients with [[irritable bowel syndrome]] (IBS) though studies to date have been inconclusive.

Naturally occurring ''Bifidobacterium'' spp. may discourage the growth of [[gram-negative bacteria|Gram-negative]] pathogens in infants.

Mother's milk contains high concentrations of lactose and lower quantities of phosphate ([[pH buffer]]). Therefore, when mother's milk is fermented by lactic acid bacteria (including bifidobacteria) in the infant's gastrointestinal tract, the pH may be reduced, making it more difficult for Gram-negative bacteria to grow.

== Bifidobacteria and the infant gut ==

The human infant gut is relatively sterile up until birth, where it takes up bacteria from its surrounding environment and its mother. The [[microbiota]] that makes up the infant gut differs from the adult gut. An infant reaches the adult stage of their microbiome at around three years of age, when their microbiome diversity increases, stabilizes, and the infant switches over to solid foods. Breast-fed infants are colonized earlier by ''Bifidobacterium'' when compared to babies that are primarily formula-fed. ''Bifidobacterium'' is the most common bacteria in the infant gut microbiome. There is more variability in [[genotype]]s over time in infants, making them less stable compared to the adult ''Bifidobacterium''. Infants and children under three years old show low diversity in microbiome bacteria, but more diversity between individuals when compared to adults.  Reduction of ''Bifidobacterium'' and increase in diversity of the infant gut microbiome occurs with less breast-milk intake and increase of solid food intake. Mammalian milk all contain [[oligosaccharide]]s showing natural selection. Human milk oligosaccharides are not digested by enzymes and remain whole through the digestive tract before being broken down in the colon by microbiota. ''Bifidobacterium'' species genomes of ''[[Bifidobacterium longum|B. longum]], B. bifidum, [[Bifidobacterium breve|B. breve]]'' contain genes that can hydrolyze some of the human milk oligosaccharides and these are found in higher numbers in infants that are breast-fed. [[Glycan]]s that are produced by the humans are converted into food and energy for the ''B. bifidum.'' showing an example of [[coevolution]].

== Species ==

The genus ''Bifidobacterium'' comprises the following species:

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== See also ==

* [[List of bacterial vaginosis microbiota]]

* [[Prebiotic (nutrition)|Prebiotics]]

== External links ==

* [http://microbewiki.kenyon.edu/index.php/Bifidobacterium Bifidobacterium] at [http://microbewiki.kenyon.edu/ Microbe Wiki]

*[https://biomesight.com/blog/bifidobacteria-spotlight Spotlight on Bifidobacteria]

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{{Bacteria classification}}

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{{二次利用|date=20 March 2024}}

[[Category:Bifidobacteriales]]