Bifidobacterium

Bifidobacterium is a genus of Gram-positive, non-spore-forming, anaerobic bacteria in the phylum Actinobacteria. They are among the dominant groups of bacteria in the human and animal gastrointestinal tracts, especially in infants, where they can make up a large portion of the gut microbiota. They are also found in the vaginal microbiota of healthy women and in other mucosal sites.

Morphology and metabolism: Bifidobacteria are typically rod-shaped or pleomorphic and may appear branched. They are saccharolytic, fermenting carbohydrates primarily via the fructose-6-phosphate phosphoketolase pathway, a metabolism sometimes referred to as the bifid shunt. End products typically include acetate and lactate, which can contribute to lower colonic pH and inhibit pathogens. They are generally strict or highly anaerobes and are sensitive to oxygen exposure.

Ecology and health: Early-life colonization is influenced by vaginal birth and breastfeeding. In the gut, bifidobacteria support barrier function and modulate the immune system, and their metabolic activity generates short-chain fatty acids that benefit the host. They are widely used as probiotics and are frequently combined with prebiotics in synbiotic products to promote growth in the gut.

Taxonomy and applications: The genus includes species such as B. longum, B. breve, B. bifidum, B. adolescentis, and B. animalis, among others. These bacteria are generally regarded as safe and are employed in dietary supplements and some fermented foods. Evidence supports benefits for certain conditions, such as antibiotic-associated diarrhea and some aspects of infant gut health, though effects are strain- and condition-specific.

Safety: In healthy individuals, bifidobacteria are considered safe. Rare adverse events, including bacteremia or sepsis, have been reported in severely immunocompromised patients or those with invasive devices, highlighting the need for cautious use in at-risk groups.