Mutagenesis within the gastrointestinal tract determined by histidine auxotrophs of Salmonella typhimurium.

The Ames Salmonella mutants can be maintained for months within the gastrointestinal tract of otherwise germfree rats. The ingestion of various carcinogens, but not structurally related non-carcinogens, results in an increased concentration of his+ revertants in the feces. Rats, associated with strain TA1538, were also associated with either L. plantarum of B. vulgatus and with both of these strains. After 2-nitrofluorene ingestion (3.4 mg) the concentration of fecal revertants increased except in rats associated only with strains TA1538 and B. vulgatus. The concentration of B. vulgatus. The concentration of B. vulgatus in the stomach of individual rats correlated negatively with their response to 2-nitrofluorene. Since only B. vulgatus reduces nitrofluorene to the less mutagenic 2-aminofluorene, it appears that B. vulgatus diminishes the revertant response by metabolic removal of the more potent direct acting mutagen from the gut. The ingestion of 1,2-dimethylhydrazine (21 mg/kg) and azoxymethane (19 mg/kg) provokes increased fecal revertants only in some animals associated with strain TA1535 or TA100.