Lactobacillus acidophilus is a "friendly" strain of bacteria used to make yogurt and cheese. Although we are born without it, acidophilus soon establishes itself in our intestines and helps prevent intestinal infections. Acidophilus also flourishes in the vagina, where it protects women against yeast infections.

Acidophilus is one of several microbes known collectively as probiotics (literally, "pro life," indicating that they are bacteria and yeasts that help rather than harm). Others include the bacteria L. bulgaricus, L. reuteri, L. plantarum, L. casei, B. bifidus, S. salivarius, andS. thermophilus and the yeast Saccharomyces boulardii. Your digestive tract is like a rain forest ecosystem with billions of bacteria and yeasts rather than trees, frogs, and leopards. Some of these internal inhabitants are more helpful to your body than others. Acidophilus and related probiotics not only help the digestive tract function, they also reduce the presence of less healthful organisms by competing with them for the limited space available. For this reason, use of probiotics can help prevent infectious diarrhea.

Antibiotics can disturb the balance of your "inner rain forest" by killing friendly bacteria. When this happens, harmful bacteria and yeasts can move in and flourish. This can lead to vaginal yeast infections. Conversely, it appears that the regular use of probiotics can help prevent vaginal infections and generally improve the health of the gastrointestinal system. Whenever you take antibiotics, you should probably take probiotics as well and continue them for some time after you are done with the course of treatment.

Although we believe that they are helpful and perhaps even necessary for human health, we don't have a daily requirement for probiotic bacteria. They are living creatures, not chemicals, so they can sustain themselves in your body unless something comes along to damage them, such as antibiotics.

Cultured dairy products, such as yogurt and kefir, are good sources of acidophilus and other probiotic bacteria. Supplements are widely available in powder, liquid, capsule, or tablet form. Grocery stores and natural food stores both carry milk that contains live acidophilus. In addition to probiotics, related substances known as prebioticsmay enhance the colonization of healthy bacteria in the intestinal tract.140