OECD 471: Bacterial Reverse Mutation Test (Ames)

The bacterial reverse mutation test uses amino-acid requiring at least five strains of Salmonella typhimurium and Escherichia coli to detect point mutations by base substitutions or frameshifts. The principle of this bacterial reverse mutation test is that it detects mutations which revert mutations present in the test strains and restore the functional capability of the bacteria to synthesize an essential amino acid. Suspensions of bacterial cells are exposed to the test substance (liquid or solid) in the presence and in the absence of an exogenous metabolic activation system. At least five different analysable concentrations of the test substance should be used. The recommended maximum test concentration for soluble non-cytotoxic substances is 5 mg/plate or 5 ml/plate. There are two methods: the plate incorporation method and the preincubation method. For both techniques, after two or three days of incubation at 37°C, revertant colonies are counted and compared to the number of spontaneous revertant colonies on solvent control plates.