Bacillus subtilis is a rod-shaped, gram-positive bacterium. It is found in soil and the gastrointestinal tract of ruminants and humans. Bacillus subtilis is considered as an ideal probiotic as it is found as a normal gut commensal in humans and it has the ability to tolerate extreme environmental conditions. It is considered a tough probiotic because it can form a protective endospore to keep itself alive almost indefinitely. It tolerates extreme environmental conditions of temperature and desiccation. It is stable at extreme pH levels and high temperatures, can survive desiccation as well as challenging storage/ manufacturing conditions, and the gastric environment in the stomach.