What is Reuteri? Pronounced roy'-tur-eye, this unique lactobacillus is naturally found in human breast milk, and is one of the first defenses a nursing mother passes to her child. When taken as a supplement, reuteri colonizes in the intestine and provides healthy benefits. Why take Primadophilus® Reuteri? Maintaining a proper level of Lactobacillus reuteri and other lactobacillus&bifidobacterium cultures may help maintain optimal bowel health.