Lactobacillus acidophilus: This bacteria is part of the normal flora of the human and animal mouth, intestinal tract, and vagina. As normal flora, it helps to prevent overgrowth of potentially harmful bacteria by maintaining an acidic environment. Acidophilus and some related bacteria are considered to be "probiotic" because they may help the body maintain or restore its normal balance of helpful bacteria. The use of antibiotics can decimate the normal flora in the body. Some healthcare professionals recommend probiotics to counter the side effect of antibiotic use. L. acidophilus is found in milk and fermented products like yogurt with "active cultures" and in the form of supplements.
See also probiotics.