Aim: Detection of bacterial genotoxicity in a 96-well screening system.

Background information: Test items showing genotoxic activity are considered to have the potential to be human carcinogens and/or mutagens, this being an important liability for drug development.

In the SOS/umu assay, Salmonella typhimurium bacterial strain TA1535/pSK1002 carries plasmid pSK1002 which bears umuD and umuC genes (involved in the SOS pathway of DNA repair) fused with lacZ, the structural gene for b-galactosidase. Exposure to DNA-damaging agents induces the transcription of the umuDC operon fused gene producing a hybrid protein with ß-galactosidase activity. The b-galactosidase metabolization of the colorless substrate ortho-Nitrophenyl-β-galactoside (ONPG) into galactose and the yellowish coloured ortho-nitrophenol, allows the colorimetric quantitative assessment of the enzymatic activity, that correlates with DNA damage.

This miniaturized bacterial genotoxicity screening system shows a high correlation with the Ames test and allows the early screening of a high number of test items, in a reduced time and with a limited amount of compound (Oda, 1985; Reifferscheid, 1996; Walmsley, 2005).