Bifidobacterium bacteria, computer illustration. Bifidobacteria are gram-positive anaerobic bacteria that live in the gastrointestinal tract, vagina and mouth. They have a unique hexose (sugar) metabolism, called the bifid shunt, which can be used as a diagnostic test for bifidobacteria. Bifidobacteria are probiotic bacteria, which means that they may beneficially affect the host upon ingestion by improving the balance of the intestinal microflora.