Representative morphologic characteristics of B

''Bifidobacterium longum'' is a

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting ...

-negative, rod-shaped bacterium present in the human gastrointestinal tract and one of the 32 species that belong to the genus ''

Bifidobacterium ''Bifidobacterium'' is a genus of gram-positive, nonmotile, often branched anaerobic bacteria. They are ubiquitous inhabitants of the gastrointestinal tract though strains have been isolated from the vagina and mouth ('' B. dentium'') of mamma ...

''. It is a microaerotolerant

anaerobe An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenat ...

and considered to be one of the earliest colonizers of the gastrointestinal tract of infants. When grown on general anaerobic medium, ''B. longum'' forms white, glossy colonies with a convex shape. ''B. longum'' is one of the most common bifidobacteria present in the gastrointestinal tracts of both children and adults. ''B. longum'' is non-pathogenic, is often added to food products, and its production of

lactic acid Lactic acid is an organic acid. It has the molecular formula C3H6O3. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as wel ...

is believed to prevent growth of pathogenic organisms.

Classification

In 2002, three previously distinct species of ''Bifidobacterium'', ''B. infantis'', ''B. longum'', and ''B. suis'', were unified into a single species named ''B. longum'' with the biotypes ''infantis, longum,'' and ''suis'', respectively. This occurred as the three species had extensive

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

similarity including a

16S rRNA 16S ribosomal RNA (or 16Svedberg, S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as ...

gene sequence similarity greater than 97%. In addition, the three original species were phenotypically difficult to distinguish due to different

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

fermentation patterns among strains of the same species. As probiotic activity varies among strains of ''B. longum'', interest exists in the exact classification of new strains, although this is made difficult by the high gene similarity between the three biotypes. Currently, strain identification is done through

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

(PCR) on the subtly different 16S rRNA gene sequences.

Environment

''B. longum'' colonizes the human gastrointestinal tract, where it, along with other ''Bifidobacterium'' species, represents up to 90% of the bacteria of an infant's gastrointestinal tract. This number gradually drops to 3% in an adult's gastrointestinal tract as other enteric bacteria such as ''

Bacteroides ''Bacteroides'' is a genus of Gram-negative, obligate anaerobic bacteria. ''Bacteroides'' species are non endospore–forming bacilli, and may be either motile or nonmotile, depending on the species. The DNA base composition is 40–48% GC. Un ...

'' and '' Eubacterium'' begin to dominate. Some strains of ''B. longum'' were found to have high tolerance for

gastric acid Gastric acid or stomach acid is the acidic component – hydrochloric acid – of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other a ...

and

bile Bile (from Latin ''bilis''), also known as gall, is a yellow-green/misty green fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is primarily composed of water, is pro ...

, suggesting that these strains would be able to survive the gastrointestinal tract to colonize the lower small and large

intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...

. The persistence of ''B. longum'' in the gut is attributed to the glycoprotein-binding fimbriae structures and bacterial polysaccharides, the latter of which possess strong electrostatic charges that aid in the adhesion of ''B. longum'' to intestinal

endothelial cells The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the res ...

. This adhesion is also enhanced by the fatty acids in the

lipoteichoic acid Lipoteichoic acid (LTA) is a major constituent of the cell wall of gram-positive bacteria. These organisms have an inner (or cytoplasmic) membrane and, external to it, a thick (up to 80 nanometer) peptidoglycan layer. The structure of LTA varies b ...

of the ''B. longum'' cell wall.

Metabolism

''B. longum'' is considered to be a scavenger, possessing multiple

catabolic Catabolism () is the set of metabolic pathways that breaks down molecules into smaller units that are either oxidized to release energy or used in other anabolic reactions. Catabolism breaks down large molecules (such as polysaccharides, lipi ...

pathways to use a large variety of nutrients to increase its competitiveness among the gut microbiota. Up to 19 types of

permease The permeases are membrane transport proteins, a class of multipass transmembrane proteins that allow the diffusion of a specific molecule in or out of the cell in the direction of a concentration gradient, a form of facilitated diffusion Facil ...

exist to transport various carbohydrates with 13 being ATP-binding cassette transporters. ''B. longum'' has several glycosyl

hydrolases In biochemistry, hydrolases constitute a class of enzymes that commonly function as biochemical catalysts that use water to break a chemical bond: :\ce \quad \xrightarrowtext\quad \ce This typically results in dividing a larger molecule into s ...

to metabolise complex oligosaccharides for carbon and energy. This is necessary as mono- and disaccharides have usually been consumed by the time they reach the lower gastrointestinal tract where ''B. longum'' resides. In addition, ''B. longum'' can uniquely ferment galactomannan-rich

natural gum Natural gums are polysaccharides of natural origin, capable of causing a large increase in a solution's viscosity, even at small concentrations. They are mostly gum (botany), botanical gums, found in the woody elements of plants or in seed coati ...

using glucosaminidases and alpha-mannosidases that participate in the fermentation of glucosamine and mannose, respectively. The high number of genes associated with oligosaccharide metabolism is a result of

gene duplication Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene ...

and

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the e ...

, indicating that ''B. longum'' is under selective pressure to increase its capability to compete for various substrates in the gastrointestinal tract. Furthermore, ''B. longum'' possesses hydrolases, deaminases, and dehydratases to ferment

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...

. ''B. longum'' also has bile salt hydrolases to hydrolyze bile salts into amino acids and bile acids. The function of this is not clear, although ''B. longum'' could use the amino acids products to better tolerate bile salts. Among six tested strains of ''Bifidobacterium'' from human gut, only ''B. longum'' biotype ''infantis'' demonstrated significant growth on

human milk oligosaccharide Human milk oligosaccharides (HMOs), also known as human milk glycans, are short polymers of Monosaccharide, simple sugars that can be found in high concentrations in Breast milk, human breast milk. Human milk oligosaccharides promote the developmen ...

s as the sole carbon source.

Pathogenesis

A number of cases of ''B. longum'' infection have been reported in the scientific literature. These are primarily cases in preterm infants that are undergoing probiotic treatment, although there are also reports of infection in adults. Infection in preterm infants manifests as bacteremia or necrotizing enterocolitis, while in adults there have been reports of sepsis and peritonitis.

Research

''B. longum'' is a constituent in VSL#3.

Immune system regulation

The use of ''B. longum'' was shown to shorten the duration and minimize the severity of symptoms associated with the

common cold The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...

with a similar effect to that of

neuraminidase inhibitors Neuraminidase inhibitors (NAIs) are a class of drugs which block the neuraminidase enzyme. They are a commonly used antiviral drug type against influenza. Viral neuraminidases are essential for influenza reproduction, facilitating viral budding fro ...

for influenza.

Bifidobacterium longum 35624

''Bifidobacterium longum'' ssp. ''longum'' 35624, previously classified as ''Bifidobacterium longum'' ssp. ''infantis'' 35624, classified as ''Bifidobacterium infantis'' 35624 before that and still marketed as such. It is sold under the brand name Align in the US and Canada and Alflorex in Ireland, the UK and other European countries. It is patented. This strain was isolated directly from the epithelium of the terminal

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...

of a healthy human subject, and is one of the most researched probiotic strains. Large scale clinical trials have shown that the strain is effective in controlling the symptoms of IBS including bloating, diarrhoea, abdominal pain and discomfort.

Bifidobacterium longum BB536

Bifidobacterium longum BB536 was discovered in the intestines of healthy breastfed infants in 1969. It is often used in nutritional supplement. In some small clinical trials, it has been shown to help defecation and relieve lactose intolerance symptoms.

References

External links

Type strain of ''Bifidobacterium longum'' at Bac''Dive'' – the Bacterial Diversity Metadatabase

On: sci-news. Dec 22, 2020. About APC1472. * {{Taxonbar, from=Q4904768 Bifidobacteriales Gut flora bacteria Probiotics Bacteria described in 1963