Lactobacillus reuteri is one of very few probiotic species whose natural habitat is the digestive tract and it is therefore especially well adapted to thrive in this kind of environment. It is among the first bacterial species to become naturally established in the normal microbiota of the newborn. Most other probiotic strains are only temporary or transient inhabitants of the gastrointestinal tract, derived from the intake of food.
In humans Lactobacillus reuteri has been isolated from:
- Breast milk
- The mouth
- The stomach
- The small intestine (duodenum and ileum)
- The colon (large intestine)
- The vagina