Critical features of bacterial mutation assays.
This review discusses features of the standard protocols currently used in bacterial mutation assays which can have a critical effect upon the test outcome. Such features if not strictly controlled may affect the results qualitatively as well as quantitatively. These include the dose-intervals of the test compound used; the number of bacterial cells exposed to the test compound; the phase of growth such cells are in during exposure; and the length of time that the cells are exposed prior to the addition of soft agar (in the Salmonella/plate incorporation assay). The following possible modulating effects will also be discussed: the nature of the solvent used; the nature and quantity of the exogenous metabolizing system (usually liver S9-fraction) and the quantity of amino-acid (e.g. histidine) within the test system being that either deliberately added or present unavoidably within the test sample (e.g. biological fluids). If bacterial mutagenicity assays are to realize their full potential for the detection of genotoxic carcinogens, the use of rigid protocols should be discouraged. Where possible, consideration of the compound's structure should lead to the employment of the optimal protocol for the detection of genotoxic carcinogens within that chemical class. The relative speed and low cost of bacterial assays should be exploited in this way to avoid the generation of false negative results during the primary screening of novel compounds.