Bifidobacterium
Bifidobacterium is a genus of Gram-positive, anaerobic, branched-rod bacteria, in the phylum Actinobacteria. It is one of the first colonizers of a baby's gut, especially in breastfed infants. There, strains like B. longum subsp. infantis are uniquely able to digest the special sugars in breast milk (human milk oligosaccharides, or HMOs). Their main products are acetate and lactate (made by a pathway called the bifid shunt). Those acidify the gut and hold pathogens back. Levels drop sharply after weaning, and again after your 70s. In older adults, low levels have been linked to frailty, a leakier gut, and more inflammation. (Cause is hard to prove, though.) Several species stand out as probiotics: B. longum, B. lactis, B. bifidum, and B. breve. They are among the most-studied and most-used. Clinical evidence supports modest benefits for antibiotic-associated diarrhea, infant colic, irritable bowel syndrome, and rotavirus diarrhea. Effects in healthy adults are generally weaker.
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