A gram-positive (see GRAM'S STAIN), rod-shaped, non-motile bacterium (see BACTERIA). It produces LACTIC ACID by fermenting CARBOHYDRATE. Lactobacilli are found in fermenting animal and plant products, especially dairy products; they also occur in the GASTROINTESTINAL TRACT and the VAGINA. L. acidophilus occurs in milk and is a contributory cause to the development of dental caries (see TEETH, DISORDERS OF).