Color enhanced scanning electron micrograph (SEM) of the bacteria Lactobacillus acidophilus. A spirochete bacteria can also be seen at center. L. acidophilus occur naturally in the gut and are considered a probiotic, or beneficial bacteria, as they act to keep our intestinal flora in check. L. acidophilus also form the predominant fauna in the vagina. These bacteria ferment lactic acid and produce an acidic environment that inhibits the growth of other bacteria and protects the vagina from pathogenic infection. L. acidophilus are also found in dairy products and are used in the manufacture of yogurt.