Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil, the gastrointestinal tract of ruminants and humans. It is considered the best studied gram positive bacterium and one of the bacterial champions in secreted enzyme production. Bacillus subtilis is a model organism used to study bacterial chromosome replication. Bacillus subtilis were popular worldwide before the introduction of antibiotics as an immunostimulatory agent to aid treatment of gastrointestinal and urinary tract diseases.