The Salmonella typhimurium strains (TA97A, TA98, TA100, TA102, and TA1535) have been employed for Ames mutagenicity or bacterial reverse mutation test. They have been chosen based on their sensitivity to mutations. The tester strains due to a mutation in their gene sequence requires histidine for growth. In general, the test item at defined concentrations is mixed with tester strains with minimum amount of histidine present, which is insufficient for normal growth of bacteria. If, the strains underwent a reverse mutation, the visible bacterial colonies will grow on agar plate. The test is performed both with and without S9 activation system.
