BackgroundHydrogen sulfide (H2S) serves as a mammalian cell-derived gaseous neurotransmitter. The intestines are exposed to a second source of this gas by sulfate-reducing bacteria (SRB). Bismuth subsalicylate binds H2S rendering it insoluble. The aim of this study was to test the hypothesis that SRB may slow intestinal transit in a bismuth-reversible fashion. MethodsEighty mice were randomized to five groups consisting of Live SRB, Killed SRB, SRB+Bismuth, Bismuth, and Saline. Desulfovibrio vulgaris, a common strain of SRB, was administered by gavage at the dose of 1.0x10(9) cells along with rhodamine, a fluorescent dye. Intestinal transit was measured 50minutes after gavage by euthanizing the animals, removing the small intestine between the pyloric sphincter and the ileocecal valve and visualizing the distribution of rhodamine across the intestine using an imaging system (IVIS, Perkin-Elmer). Intestinal transit (n=50) was compared using geometric center (1=minimal movement, 100=maximal movement). H2S concentration (n=30) was also measured when small intestinal luminal content was allowed to generate this gas. Key ResultsThe Live SRB group had slower intestinal transit as represented by a geometric center score of 40.25.7 when compared to Saline: 73.6 +/- 5.7, Killed SRB: 77.9 +/- 6.9, SRB+Bismuth: 81.0 +/- 2.0, and Bismuth: 73.3 +/- 4.2 (P<.0001). Correspondingly, the Live SRB group had the highest luminal H2S concentration of 4181.0 +/- 968.0ppb compared to 0 +/- 0ppb for the SRB+Bismuth group (P<.0001). Conclusions & InferencesLive SRB slow intestinal transit in a bismuth-reversible fashion in mice. Our results demonstrate that intestinal transit is slowed by SRB and this effect could be abolished by H2S-binding bismuth.