INHIBITION OF THE SPONTANEOUS MUTAGENICITY IN SALMONELLA-TYPHIMURIUM TA102 AND TA104

Thirty-four compounds belonging to various chemical classes were assay ed for the ability to modulate the 'spontaneous' mutagenicity in strai n TA104 of S. typhimurium, and 17 of them were also assayed in TA102. Ah test agents, many of which were already known or suspected to act a s 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 consider able proportion of test compounds decreased the number of spontaneous revertants in TA104 (44.1%) and/or TA102 (41.2%) to a significant exte nt, with dose-related and reproducible effects. In almost all cases th e antimutagenic effect was genuine and not related to bacterial killin g or growth inhibition. The results obtained suggest that the DNA repa ir background plays a prominent role in the genesis of spontaneous mut ations in these strains, containing the hisG428 mutation which is typi cally reverted by oxidative mutagens. Due to its theoretical and pract ical implications, the finding that several chemopreventive agents can attenuate the rate of spontaneous reversion deserves attention.