Inhibition of the 'spontaneous' mutagenicity in Salmonella typhimurium TA102 and TA104.

Thirty-four compounds belonging to various chemical classes were assayed for the ability to modulate the 'spontaneous' mutagenicity in strain TA104 of S. typhimurium, and 17 of them were also assayed in TA102. All test agents, many of which were already known or suspected to act as inhibitors of induced mutagenicity, had been previously monitored in our laboratory for antimutagenicity towards either 4-nitroquinoline 1-oxide in TA100 and/or cigarette smoke in TA98 with S9 mix. A considerable proportion of test compounds decreased the number of spontaneous revertants in TA104 (44.1%) and/or TA102 (41.2%) to a significant extent, with dose-related and reproducible effects. In almost all cases the antimutagenic effect was genuine and not related to bacterial killing or growth inhibition. The results obtained suggest that the DNA repair background plays a prominent role in the genesis of spontaneous mutations in these strains, containing the hisG428 mutation which is typically reverted by oxidative mutagens. Due to its theoretical and practical implications, the finding that several chemopreventive agents can attenuate the rate of spontaneous reversion deserves attention.