Sensitivity of different E. coli and Salmonella strains in mutagenicity testing calculated on the basis of selected literature.

Two microbial screening test systems for gene (point) mutations, the Salmonella typhimurium assay (TA1535, TA1537, TA1538, TA98 and TA100) and the Escherichia coli WP2 reverse-mutation system (WP2, WP2uvrA, WP2pKM101 and WP2uvrApKM101), were compared with regard to sensitivity toward a broad spectrum of compounds that cause base-pair or frameshift mutations and that have known carcinogenic qualities. Based on available published literature we found that all 44 carcinogens and 9 non-carcinogens examined in both test systems also met with criteria for data acceptance drawn up by us. The results obtained are: firstly, that the Salmonella assay is decidedly better validated than the E. coli WP2 test; and secondly, that the E. coli test system sensitivity (91%) is fully on a par with the sensitivity of the Salmonella assay (72%). This last is in divergence from earlier reports, e.g. Brusick et al. (1980), and this difference must be ascribed to the new plasmid-containing strains. The many compounds not tested in the E. coli department result in fewer false negatives in the E. coli test system and their omission constitutes a bias in favour of the E. coli assay. By eliminating compounds that are negative in Salmonella and dropped from the WP2 analysis owing to insufficient data, the sensitivity of the Salmonella system is raised to 84% as compared with 91% for the WP2 assay. The results further indicate that some of the tester strains are superfluous, and show an exceedingly sensitive test can be performed by combining the best tester strains from the two test systems.