Lactobacillus reuteri is a probiotic lactic acid bacteria that is a permanent resident in the guts of humans, though it is not found in every individual. Unlike some of the other bacteria that exist in the human system for a particular period of time, Lactobacillus reuteri does not leave the system. It is also found in human breast milk.
Beneficial effects: Helps in boosting the immune system, and also has anti-gas properties.
Sources: Capsules, yogurt, breast milk, and cheese.