Assessing the effect of colony counting methods and genetic drift on Ames bioassay results

Accuracy of automatic colony counters and variation among subcultures of the Salmonella tester strains are two factors that cause variation within the Ames bioassay. This paper examines these potential sources of variation. In contrast to results seen by other researchers, this genetic drift study demonstrated that except for TA100 the subcultures of tester strains from four research laboratories are very stable in biochemical characteristics measured using Analytical Profile Index (API) strips. This study also documented the levels of accuracy for hand- and automatic-counting techniques, and provides a simple method for generating acetate calibration transparencies for use with most colony counters.