Bifidobacteria, coloured scanning electron micrograph (SEM). 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 because it is not found in other gram-positive intestinal bacteria. Bifidobacteria are probiotic friendly bacteria, which means that they may beneficially affect the host upon ingestion by improving the balance of the intestinal microflora. Magnification: x13,300 when printed at 10 centimetres across.