Collaborative study of interlaboratory variability in Salmonella typhimurium TA102 and TA2638 and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101. Association of Microbial Mutation Testing Laboratory C.O.

A collaborative study of interlaboratory variability in bacterial mutagenicity induced by mitomycin C (MMC) and bleomycin (BLM) was performed using the four strains Salmonella typhimurium TA102 and TA2638 and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101. Thirteen laboratories participated in this study. The four strains and two chemicals were sent from a central source to each laboratory. Each strain was cultured in nutrient broth containing antibiotics and laboratories were requested to ensure that the spontaneous counts for marker check fell within a specified range in the preparation of the original stock culture. Concerning the response to the chemicals, most interlaboratory variability was within a 4-fold range for tests with TA102, TA2638 and WP2/pKM101. From the results of the statistical analysis using the linear regression test, positive results in TA102, TA2638 and WP2/pKM101 and negative results in WP2 uvrA/pKM101 were obtained by MMC testing in all of the laboratories. On the other hand, with BLM testing, considerable interlaboratory variability was observed between the strains, largely because of the variation in results of the repeat experiments. Overall mean spontaneous revertant counts in all laboratories were within acceptable ranges for all four bacterial strains. In conclusion, it is judged that among Japanese laboratories, there is excellent agreement in the tested response of these bacterial strains to a strong mutagen such as MMC, as well as uniformity in the spontaneous reversion rates. However, for chemicals such as BLM that induce a weak response, it may be necessary to repeat experiments several times to obtain clear results. In this study, TA102 was shown to be a useful strain for routine mutagenicity testing. This necessitated control over culture maintenance by the addition of tetracycline and strict selection in the preparation of the original stock cultures.