Observed OTU counts on proton pump inhibitors. Plot depicts patient observed-OTU counts at start of treatment, 1 week into treatment, and at the end of the 1-month program, followed by final collection 1 month after ceasing PPI usage. Five first-incidence C. difficile patients had stool isolated and sequenced to represent the C. difficile cohort. Black horizontal bars represent within-group means. All statistical tests using matched-pair healthy volunteers used Wilcoxon signed rank; statistical tests between healthy volunteer groups (*p <0.05, **p <0.005) and C. difficile group used Wilcoxon rank sum (§p <0.05, §§p <0.01).