Lactobacillus is a member of the lactic acid bacteria group a genus of Gram positive anaerobic bacteria. Lactobacillus is named such because most of the bacteria in the group convert lactose and other sugars to lactic acid. In humans they are present in the gastrointestinal tract, where they make up a small portion of the gut flora. Many species are found in decaying plant material, causing fermentation. The metabolism by these bacteria produces lactic acid and makes its environment acidic, reducing the growth of other bacteria species.