Evaluation of the SOS/umu-test post-treatment assay for the detection of genotoxic activities of pure compounds and complex environmental mixtures

This study presents an evaluation of the SOS/umu-test after introducing an additional dilution and incubation in the post-treatment assay. This treatm ent reduces the influence of coloured test compounds that otherwise affect the colorimetric determination of the beta-galactosidase activity and the b acterial growth measurement during the testing of complex environmental sam ples. The post-treatment assay significantly increased the beta-galactosida se activity and consequently the enzyme induction ratios at higher doses of model genotoxins 4-nitroquinoline-N-oxide, N-methyl-N'-nitro-N-nitrosoguan idine, 2-aminoanthracene, benzo(a)pyrene with low or no effect on the sensi tivity of the test itself. On the other hand tests of environmental extract s indicated significant increases in sensitivity after additional incubatio n. 4-Nitroquinoline-N-oxide treatments of bacteria in the test affected cel l division and caused filamentous growth. The size of filamentous bacteria and incidence rate of the length categories was positively correlated with the concentrations of genotoxins. Presence of filamentous tester bacteria p roved induction of SOS response and genotoxic activity of environment sampl es in SOS/umu-test. (C) 2000 Published by Elsevier Science B.V. All rights reserved.