Bifidobacterium Longum

 is a Gram-positive, catalase-negative, rod-shaped bacterium present in the human gastrointestinal tract and one of the 32 species that belong to the genus Bifidobacterium. It is a microaerotolerant anaerobe and considered to be one of the earliest colonizers of the gastrointestinal tract of infants.

While is not significantly present in the adult gastrointestinal tract, it is considered part of the gut microbiota and its production of lactic acid is believed to prevent growth of pathogenic organisms. is non-pathogenic and is often added to food products.