Bifidobacteria

Bifidobacteria are a group of Gram-positive, non-spore-forming, non-motile bacteria that typically appear as irregular, bifurcating rods. They belong to the genus Bifidobacterium in the family Bifidobacteriaceae, within the phylum Actinobacteria. Many species are anaerobic or aerotolerant, and they are commonly found in the gastrointestinal tracts of humans and other mammals, as well as in some fermented foods. In humans, bifidobacteria are particularly abundant in the infant gut, where growth is supported by human milk oligosaccharides.

Metabolically, bifidobacteria are known for the bifid shunt, a unique fructose-6-phosphate phosphoketolase pathway that yields acetate and lactate as major end products. This metabolic profile can support gut health by providing cross-feeding substrates for other microbes and contributing to gut acidity and pathogen resistance. They generally prefer complex carbohydrates and can utilize a range of prebiotics such as inulin-type oligosaccharides.

Several strains are used as probiotics in foods and supplements. Evidence supports potential benefits including modulation of the immune system, enhancement of gut barrier function, and competition with pathogens. They have been studied for prevention of antibiotic-associated diarrhea and for benefits in certain inflammatory and metabolic conditions, though effects are strain- and context-dependent. Safety is favorable for most individuals, but infections have been reported rarely in severely immunocompromised people.

Prominent human-associated species include B. longum, B. breve, B. adolescentis, B. bifidum, B. animalis, and B. infantis; together they form a diverse group with varying metabolic capabilities and habitat preferences. They are generally Gram-positive, non-spore-forming, and catalase-negative, and many species exhibit strain-level differences in probiotic properties.

Ongoing whole-genome sequencing and functional studies continue to refine taxonomy and understand mechanisms by which bifidobacteria influence host health.