Comparative investigation on the mutagenicities of organophosphate, phthalimide, pyrethroid and carbamate insecticides by the Ames and lactam tests.

The Salmonella lactam test is a newly developed method for detecting genotoxins. This technique is based on the ability of DNA damaging agents to reverse expression of the beta-lactamase gene, an important gene that enables microbes to resist beta-lactam antibiotics. A construct p-SELECT Control DNA plasmid containing a beta-lactamase gene site was constructed in many mutant forms, including point and frameshift mutants. These mutant constructs were introduced into Salmonella tester strains whose mutagenicity is based on their ability to reverse expression of the beta-lactamase gene. Fourteen pesticides were evaluated for genotoxicity using our newly developed Salmonella typhimurium strains JK947 and JK3, which are useful for detecting base substitution mutations. Six pesticides, namely allethrin, captan, folpet, monocrotophos, acephate and carbofuran, proved highly mutagenic in strain JK947, while the first four pesticides were more weakly mutagenic in strain JK3. In comparison, results from the Ames test show strain JK947 to be more sensitive to these pesticides than strains TA100 and TA1535. Strains TA98 and JK1 proved insensitive to allethrin, captan, folpet, acephate, carbofuran and monocrotophos. Among the many advantages of the lactam test are: large numbers of cells can treated and the test is operationally simple and inexpensive; revertant colonies form faster in the lactam test (16 h) than in the Ames test (48 h); the lactam test can detect mutagens present in biological specimens contaminated by histidine and biotin, samples that may give false positive results in the Ames test.