Bifidobacterium longum

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 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. Currently, strain identification is done through polymerase chain reaction (PCR) on the subtly different 16S rRNA gene sequences. B. infantis is unique in its ability to digest and consume human milk oligosaccharides (HMOs). The presence of B. infantis in the gut of infants proves to have many health benefits. It has a competitive advantage which results in less diversity in the infant gut microbiota and therefore fewer luminal pathogens. It also decreases intestinal permeability while increasing stability of tight junction proteins. It promotes the maturation of the innate immune response and promotes anti-inflammatory properties. Therefore, premature infants without B. infantis, have gut dysbiosis and an increased risk of necrotizing enterocolitis and late-onset sepsis. Currently, there is research on the use of probiotics with B. infantis for premature infants. == 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. 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. B. longum has several glycosyl hydrolases to metabolise complex oligosaccharides for carbon and energy. Among six tested strains of Bifidobacterium from human gut, only B. longum biotype infantis demonstrated significant growth on human milk oligosaccharides 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 ==

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. Bifidobacterium longum BB536 Bifidobacterium longum BB536 was discovered in the intestines of healthy breastfed infants in 1969. In some small clinical trials, it has been shown to help defecation in elderly patients with chronic constipation. == See also ==