are the predominant resident organism found in the large intestine of breast-fed infants, and are a major component of adolescent and adult large intestine microflora. The number of these anaerobic bacteria usually decline with age and in various conditions of ill-health. Bifidobacteria help prevent colonization of the intestine by invading pathogenic bacteria or yeasts with which they compete for nutrients and attachment sites. These bacteria are also important in the production of B vitamins.