Quantitation of the relationship between tester cell number inoculated and SOS-inducing potency of 4-nitroquinoline-1-oxide (4-NQO) in an automated version of the SOS chromotest.

The SOS chromotest is a simple quantitative short-term bacterial assay for the detection of genotoxic activity of pure compounds or complex samples. On the basis of consecutive experiments aimed at demonstrating the relationship between the inoculum size and the outcome of the test using 4-nitroquinoline-1-oxide (4-NQO) as model genotoxin. It is shown that within the suitable range of the cell number there is a negative correlation between the number of tester cells and test sensitivity. Moreover, it could be demonstrated that the peak of the dose response curve, i.e., the maximal induction factor, is systematically influenced by the actual value of the ratio of beta-galactosidase to alkaline phosphatase enzyme activities at a 4-NQO concentration of zero. Last but not least, some simple statistical data describing the performance of the automated version of the SOS chromotest are also given.