type species of the genus Bifidobacterium; it is found in the feces and alimentary tract of breast- and bottle-fed infants and of older people, rats, turkeys, and chickens; also found in the rumen of cattle; pathogenicity for humans and other animals is rare. Associated with a growth factor belonging to a group of N-containing polysaccharides with a high hexosamine content and known as bifidus factor.