Collaborative study of interlaboratory variability in Salmonella typhimurium TA102 and TA2638 and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101

A collaborative study of interlaboratory variability in bacterialmutagenicity induced by mitomycin C (MMC) and bleomycin (BLM)was performed using the four strains Salmonella typhimuriumTA102 and TA2638 and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101.Thirteen laboratories participated in this study. The four strainsand two chemicals were sent from a central source to each laboratory.Each strain was cultured in nutrient broth containing antibioticsand laboratories were requested to ensure that the spontaneouscounts for marker check fell within a specified range in thepreparation of the original stock culture. Concerning the responseto the chemicals, most interlaboratory variability was withina 4-fold range for tests with TA102, TA2638 and WP2/pKM101.From the results of the statistical analysis using the linearregression test, positive results in TA102, TA2638 and WP2/pKM101and negative results in WP2 uvrA/pKM101 were obtained by MMCtesting in all of the laboratories. On the other hand, withBLM testing, considerable interlaboratory variability was observedbetween the strains, largely because of the variation in resultsof the repeat experiments. Overall mean spontaneous revertantcounts in all laboratories were within acceptable ranges forall four bacterial strains. In conclusion, it is judged thatamong Japanese laboratories, there is excellent agreement inthe tested response of these bacterial strains to a strong mutagensuch as MMC, as well as uniformity in the spontaneous reversionrates. However, for chemicals such as BLM that induce a weakresponse, it may be necessary to repeat experiments severaltimes to obtain clear results. In this study, TA102 was shownto be a useful strain for routine mutagenicity testing. Thisnecessitated control over culture maintenance by the additionof tetracycline and strict selection in the preparation of theoriginal stock cultures.