The Ames II Salmonella mutagenicity assay procedure was used to test 71 chemicals, and the results were compared with those from the traditional Ames Salmonella test using the NTP database as the reference. All Ames II tests were performed using a fluctuation procedure in microplate format, using TAMix for the detection of base pair substitutions and TA98 to detect frameshift mutations. There was 84% agreement between the two procedures in identifying mutagens and non-mutagens, which is equivalent to the intra- and interlaboratory reproducibility of 87% for the traditional test. The two tests also performed similarly in their predictions of rodent carcinogenicity.

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The influence of various parameters and growth conditions in the "overnight culture" of Salmonella typhimurium strains on mutagenicity test results was investigated. A number of factors were first suspected to be of some importance for the quantitative outcome of the mutagenicity test. None of them, however, was found to influence the results to such a marked extent as to be a major source of variability. Only the brand of nutrient broth used for the propagation of the bacteria proved finally to have a certain effect on the number of (spontaneous and induced) revertant colonies, although no precise and quantitative statements can be made with regard to a possible standardization of this experimental segment in the Salmonella mutagenicity test. The occurrence of such unpredictable but noticeable influences is, however, evidence for the importance of an intralaboratory optimization and standardization of all parts of the test procedure.

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