A CORRELATION OF SALMONELLA MUTAGENICITY WITH DNA-ADDUCTS INDUCED BY THE COOKED-FOOD MUTAGEN 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE

The correlation of bacterial mutagenicity with DNA adducts from the he terocyclic amine cooked-food mutagen 2-aminol-methyl-6-phenylimidazo[4 ,5-b]pyridine (PhLP) was investigated in Salmonella typhimurium strain s TA98 (uvrB deficient) and TA1978 (uvrB proficient), Bacterial cells were exposed to PhIP using a modification of the Ames/ Salmonella micr osuspension assay, Half of the cells, generated from a 90 min pre-incu bation and washing, were plated for revertant formation while the rema ining half was subjected to DNA adduct analysis via P-32-postlabeling. In TA98, DNA adducts were detected at an RAL (relative adduct labelin g) of 10 x 10(-7) and 21 X 10(-7) at PhIP concentrations of 5.5 and 17 mu M, respectively, This corresponded to 28.8 and 20.9 adducts/revert ant, respectively, These values were based on the assumption that only four repeating GC bases within a 75 DNA base region is the gene targe t site for PhIP induced mutations, In TA1978, no revertants above back ground were detected at any concentration of PhIP tested, DNA adducts, however, were detected at 11 x 10(-7) and 21 x 10(-7) adducts per nuc leotide at 223 and 1116 mu M PhIP, respectively, The lack of detectabl e revertants, but the presence of DNA adducts, suggests pre-mutational lesions did occur during the 90 min pre-incubation, Presumably, when the S9 activating system and PhIP were removed (via washing with phosp hate buffered saline) prior to plating, the cells containing an intact uvrB repair system repaired the lesions during the incubation time on the plates. In conclusion, the induction of revertants by adducts app ears quite efficient, as similar to 25 adducts are required for one mu tational event in the excision repair deficient bacteria.