''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. Gram-positive bact ...

, catalase-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 mammal ...

''. It is a microaerotolerant anaerobe 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 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 nat ...

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 m ...

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) ...

(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. Unus ...

'' 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 and bile, 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 GI tract contains all the major organs of the digestive system, in humans and ...

. 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 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 rest of the vessel ...

. 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 ...

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, lipid ...

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. The per ...

exist to transport various carbohydrates with 13 being

ATP-binding cassette The ATP-binding cassette transporters (ABC transporters) are a transport system superfamily that is one of the largest and possibly one of the oldest gene families. It is represented in all extant phyla, from prokaryotes to humans. ABC transpo ...

transporters. ''B. longum'' has several glycosyl

hydrolases Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...

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 ...

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 and

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). H ...

, 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. ''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 Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood (hematochezia). Weight loss, fever, and ...

, 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 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 from ...

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