Mutagenicity testing experiments with the Cobas Bact

The feasibility of mutagenicity assays with the Cobas Bact Automatic analyser was explored using selected model mutagens. The reduction of the latency period (the period until the growth of the mutant cells becomes optically measurable) was found to be a valid measure for the mutagenic activity of strong mutagens. For weaker mutagens an evaluation analogous to the fluctuation test seemed the more appropriate approach. The influence of various variables, such as concentration of histidine, size of inoculum, medium composition and S9 concentration, is described. Adaptation of the Cobas Bact system to the differential growth inhibition test is also mentioned.