Probiotic Gastrointestinal Health Probiotic Supplement Groundbreaking Probiotics Driven by ScienceBioGaia Gastrus is a dietary supplement containing the patented lactic acid bacterium Lactobacillus reuteri Gastrus (L.reuteri DSM 17938 and L. reuteri ATCC 6475). Because both strains in L. reuteri Gastrus naturally colonize humans they have a strong adaptation to persist and interact with humans. BioGaia Gastrus has been tested in clinical trials are proven effective and safe.