Study Product and Dosage L. reuteri Progastria consists of a mixture of two human strains of L. reuteri, L. reuteri DSM 17938 and L. reuteri ATCC PTA 6475. L. reuteri DSM 17938 is essentially the same strain as L. reuteri ATCC 55730, except that it lacks plasmids that carried antibiotic resistance traits for tetracycline and lincomycin. This strain has been extensively studied in humans of all ages. L. reuteri ATCC PTA 6475 is a new strain that was isolated from the breast milk of a nursing mother (as was L. reuteri DSM 17938).