More than 400 different kinds of bacteria live in our gastrointestinal tract. The body depends on beneficial bacteria to manufacture B vitamins as well as to produce lactase and other antibacterial substances. Lactobacillus acidophilus is the friendly bacteria in the upper intestinal tract. It helps reduce the levels of harmful bacteria and yeasts in the small intestine and also produces lactase, an enzyme which is important in the digestion of milk. During digestion, L. acidophilus is also involved in the production of B vitamins (niacin, folic acid, and pyridoxine).