Bifidobacterium

Bifidobacterium is a genus of Gram-positive, anaerobic, non-motile, branched-rod bacteria belonging to the phylum Actinobacteria (Actinomycetota); it is among the first colonisers of the neonatal gut, particularly in breastfed infants, where strains such as B. longum subsp. infantis are uniquely equipped to metabolise human milk oligosaccharides (HMOs). Their core metabolic products include acetate and lactate (via the bifid shunt, a fructose-6-phosphate phosphoketolase pathway), acidifying the intestinal environment and suppressing pathogens. Abundance declines markedly after weaning, with a further sharp decline after the seventh decade of life; reduced Bifidobacterium abundance in older adults has been associated with frailty, increased intestinal permeability and heightened systemic inflammation, though causal interpretation remains challenging. Several species — particularly B. longum, B. lactis, B. bifidum and B. breve — are among the most extensively studied and commercially used probiotic organisms, with clinical evidence supporting modest benefits in antibiotic-associated diarrhoea, infant colic, irritable bowel syndrome and rotavirus-associated diarrhoea; effects in healthy adults are generally less pronounced.