Ames Test

The Ames test is used to evaluate whether a certain substance could be a possible carcinogen - a substance capable of causing cancer. The test uses strains of bacterium Salmonella typhimurium that carry a mutation that makes them unable to synthesize the amino acid histidine.

The bacteria are placed on two plates. One plate serves as a control plate and does not contain any mutagenic substances. The second plate contains the tested substance. If the tested substance is, in fact, mutagenic, the bacteria on the plate are going to undergo a reverse mutation that will make them capable of synthesizing histidine again. As a result, their colonies are going to grow significantly. The bacteria on the control plate are also going to grow, however, only as a result of spontaneous mutations. As these are much less frequent, the colonies are going to be much smaller.

If there are large colonies of bacteria on the test plate, the substance is considered mutagenic and possibly also carcinogenic. It is important to realise, however, that the test only serves as evidence of the substance being mutagenic. Although mutagens are usually also carcinogens, substances need to be further tested to be considered carcinogenic.

References:
Pierce, B. A. (2019). Genetics: A Conceptual Approach (Seventh ed.). W. H. Freeman.
Snustad, D. P., & Simmons, M. J. (2012). Principles of Genetics. Wiley