The AMES test also known as bacteria reversed mutation assay is used to evaluate the mutagenic properties of test articles. The test was first developed by Bruce Ames in 1974 (Krebsfaenger). The amino acid dependent strain of S. typhimurium and E. coli are used in this experiment where in the absence of the external histidine source, the cells cannot grow to form colonies. Specifically these strains of Salmonella are defective in 1. ) Repair of mutations (uvrB) and 2. A rfa mutation (eliminating a portion of lipolysaccharide (a coating of outer bacterial surface)). The rfa mutation here fulfills two purposes: 1. ) Helps Salmonella in growing in presence of sodium desoxycholate or crystal violet. and 2. ) Increases the cell permeability allowing more mutagen to enter the cell. The lack of uvrB gene in the decreases the rate of repair mechanism of mutations occurring resulting in the increased incidences of occurring mutations. These auxotrophic strain cannot grow on the media without histidine and biotine (due to uvrB).
