''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 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 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 (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'' and ''
Eubacterium
''Eubacterium'' is a genus of Gram-positive bacteria in the family Eubacteriaceae. These bacteria are characterised by a rigid cell wall
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It c ...
'' 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 of the ''B. longum'' cell wall.
Metabolism
''B. longum'' is considered to be a scavenger, possessing multiple
catabolic 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 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
See also
*
Psychobiotic
Psychobiotics is a term used in preliminary research to refer to live bacteria that, when ingested in appropriate amounts, might confer a mental health benefit by affecting microbiota of the host organism. Whether bacteria might play a role in t ...
*
Probiotic
*
Gut flora
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 mi ...
*
Microorganism
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