Fecal hydrogen sulfide production in ulcerative colitis

Objective: Sulfide, a product of sulfate-reducing bacteria, has been proposed to play an etiologic role in ulcerative colitis. Ulcerative colitis feces have increased numbers and activity of sulfate-reducing bacteria, but only modestly increased sulfide. However, fecal sulfide exists largely in the volatile, highly toxic H₂S form that moves rapidly from feces to surrounding gas. Our aim was to quantify the fecal release of H₂S and other volatiles (CO₂, H₂, CH₄, methanethiol, and dimethylsulfide). Methods: Fecal samples from 25 subjects with ulcerative colitis and 17 controls were incubated in 4- L containers, and gas release was assessed at intervals over 24 h. Results: H₂S release by ulcerative colitis feces was elevated 3-4-fold at every measurement point compared with normal feces (p < 0.003 at 24 h). The only other significant difference was increased CO₂ release by ulcerative colitis feces at 1 h. Supplementation of fecal homogenates with sulfur-containing substrates showed that organic compounds (mucin, cysteine, taurocholate) provided more readily utilizable substrate for H₂S production than did sulfate. Conclusions: Increased H₂S release is a relatively localized metabolic aberration of ulcerative colitis feces. This increased H₂S may reflect abnormalities of the fecal bacteria and/or substrate availability.