gram-positive rod-shaped bacteria that produce lactic acid especially in milk

a "friendly" bacteria that does not cause infection, found in the digestive system and the vagina. It helps keep other infection-causing germs, such as yeast, in control. Can be found in some yogurts stating that they contain "live" bacterial culture

Lactobacillus acidophilus (L. acidophilus) is the most commonly used probiotic, or "friendly" bacteria. Such healthy bacteria inhabit the intestines and vagina and protect against the entrance and proliferation of "bad" organisms that can cause disease. This is accomplished through a variety of mechanisms. For example, the breakdown of food by L. acidophilus leads to production of lactic acid, hydrogen peroxide, and other byproducts that make the environment hostile for undesired organisms. L. acidophilus also produces lactase, the enzyme that breaks down milk sugar (lactose) into simple sugars. People who are lactose intolerant do not produce this enzyme. For this reason, L. acidophilus supplements may be beneficial for these individuals.