engineered Escherichia Coli strain developed as an indicator organism for genotoxicity testing systems, and includes a gene coding for the β-galactosidase (β-gal) enzyme tethered to an SOS promoter. When DNA damage occurs, the SOS system is activated and β-gal gets transcribed proportionally to the level of SOS induction. Even limited repairable damage to genetic material is detected by the SOS-Chromotest™ due to the placement of the β-gal gene upstream of repair enzyme genes. Therefore, a positive response is produced regardless of cellular repair being initiated and the lesion being fixed.