''Bifidobacterium longum'' is a Gram-positive,

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 t ...

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

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. While ''B. longum'' is not significantly present in the adult gastrointestinal tract, it is considered part of the

gut microbiota 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 m ...

and its production of

lactic acid Lactic acid is an organic acid. It has a molecular formula . 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 well as natu ...

is believed to prevent growth of pathogenic organisms. ''B. longum'' is non-pathogenic and is often added to food products.

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 similarity including a

16S rRNA 16S rRNA may refer to: * 16S ribosomal RNA 16 S ribosomal RNA (or 16 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 g ...

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

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ma ...

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 rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) t ...

(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. Unusu ...

'' and ''

Eubacterium ''Eubacterium'' is a genus of Gram-positive bacteria in the family Eubacteriaceae. These bacteria are characterised by a rigid cell wall. They may either be motile or nonmotile. If motile, they have a flagellum A flagellum (; ) is a hair ...

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

gastric acid Gastric acid, gastric juice, or stomach acid is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid plays a key role in digestion of proteins by activating digestive enzymes, which together break down the ...

and

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile ...

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

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, lipids, ...

pathways to use a large variety of nutrients to increase its competitiveness among the gut microbiota. Up to 19 types of permease exist to transport various carbohydrates with 13 being ATP-binding cassette transporters. ''B. longum'' has several glycosyl hydrolases 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 botanical gums, found in the woody elements of plants or in seed coatings. Human u ...

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, 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 hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

. ''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.

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. This proprietary, standardized, formulation of live bacteria may be used in combination with conventional therapies to treat ulcerative colitis, and requires a prescription.

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 viral infectious disease of the upper respiratory tract that primarily affects the respiratory mucosa of the nose, throat, sinuses, and larynx. Signs and symptoms may appear fewer than two days after exposu ...

with a similar effect to that of neuraminidase inhibitors 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 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

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