Lactobacillus acidophilus is a species of gram-positive bacteria in the genus Lactobacillus. L. acidophilus is a homofermentative, microaerophilic species, fermenting sugars into lactic acid, and grows readily at rather low pH values (below pH 5.0) and has an optimum growth temperature of around 37 °C (99 °F). L. acidophilus is found in the human and animal gastrointestinal tract and mouth. Some strains of L. acidophilus may be considered to have probiotic characteristics.