DETECTION OF CHEMICAL MUTAGENS USE OF CONCENTRATION GRADIENT PLATES IN A HIGH-CAPACITY SCREEN

Abstract

A method is described which enables rapid screening of chemicals for mutagenic potential. Ten-fold concentration gradients of test compound in agar are prepared in square petri dishes. Ten strains of bacteria [Salmonella typhimurium, Escherichia coli], including histidine auxotrophs and tryptohan auxotrophs, are streaked on the surface. In the activated phase of the test, an overlay of 9000 g [rat] liver homogenate in agar is applied to the gradient plate before the organisms are streaked. After incubation the plates are scored by observing the concentration range over which the test compound produces mutant colonies in each of the 10 organisms. With this technique, the mutagenic potential of a substance against 10 different bacterial strains can be determined using only 8 plates, with or without microsomal activation and over a 10,000-fold concentration range. The minimum concentration at which growth of the auxotroph is inhibited is noted. The method was useful for preliminary screening of large numbers of chemicals.