Characterization of a mutagenic bacterial product in human feces

Mutagens detectable with the Ames assay have been found in the feces of apparently healthy individuals and the incidence of this mutagenic activity was found to be greater in a population at high risk for colon cancer than in a population at low risk. A compound accounting for the mutagenic activity has been isolated by high performance liquid chromatography. Two closely related forms which behave identically chemically could be resolved. The compound was active on Salmonella typhimurium TA98 and TA100, had a characteristic ultraviolet absorption spectrum with maxima at about 320, 340, and 365 nm, fluoresced green in long wavelength ultraviolet light, and had the same mobility on the thin-layer chromatography as the mutagenic activity in a direct ether extract of feces. The compound was unstable in air but could be stabilized in the presence of butylated hydroxytoluene. Upon oxidation the compound lost its mutagenicity and its ultraviolet absorption spectrum underwent a blue shift so that the absorption maxima were at 295, 310, and 325 nm. Determination of the structure of the mutagen has been difficult since the compound was not volatile and production of a volatile derivative has not been successful. On thin-layer chromatography plates the compound reacted with reagents that detect chlorinated compounds. By thermal energy analysis it did not appear to contain a nitroso group. The compound increased in concentration upon anaerobic incubation of feces at 37 C and this increase was prevented by cold, air, and antimicrobial agents. This suggests to us that the fecal flora produces the compound.