A study of the heterogeneity of bacterial fluctuation-test data and the effects of auxotrophic-growth enhancement.

Microtitre fluctuation tests using Salmonella typhimurium TA100 and TA98 and Escherichia coli WP2uvrApKM101 were performed to determine the heterogeneity of spontaneous mutagenicity data and how this affects interpretation of results. Assays were performed in the absence and presence of additional amino acids to simulate the effects of the auxotrophic growth enhancement characteristic of tests of complex biological mixtures. The results indicate that the heterogeneity of the data did not depart significantly from that expected from binomial theory and that two criteria must be satisfied in order to define a positive result: (i) a net increase which significantly exceeds the background mutation and which takes account of its heterogeneity; and (ii) a statistically significant dose response.