HPi1 is a potent, selective and orally active antimicrobial against Helicobacter pylori with an IC50 of 0.24 μM and an MIC of 0.08-0.16 μg/mL. HPi1 is inactive against other bacteria, including the gut commensals Lactobacillus casei, Lactobacillus reuteri, and Bifidobacterium longum.