Ames Test - Detecting Mutagenicity; and Ethidium Bromide as a case study...
The Ames Test was developed in the 1970s by Bruce Ames. This test is a gold standard to determine the mutagenicity of substances. It is very valuable in the prelinimary studies of potentially carcinogenic and mutagenic compounds. Mutant strains of the bacterium Salmonella typhimurium (or E.coli) that are histidine auxotrophs (his-), i.e. cannot synthesise histidine from media components and therefore require incorporation of histidine into the media in order to grow, are used. Apart from the his- mutation, these bacteria also carry mutations that render DNA repair mechanisms defective and cell wall synthesis inefficient. These serve to make the cells highly sensitive to mutation. The bacteria are subjected to addition of the compound thought to be a mutagen, and then assayed on his- media. The frequency of reverse mutations (resulting in cells that do survive on histidine deficient media) are counted. This frequency is compared with frequency of spontaneous reverse mutations. An increa...