Ames – A test used to determine the effects of a chemical on the rate of mutation in bacterial cells, and hence its likely potential for causing cancer in other organisms, including humans.

Devised by US biologist Bruce Ames, it is widely used in screening chemicals occuring in the environment for possible carcinogenic activity.

The chemical being tested is applied to plates inoculated with a special mutant strain of bacteria (usually Salmonella typhimurium) that require the amino acid histidine for growth. Cells that mutate back to the wild type are detected by the occurance of colonies able to synthesise their own histidine and therefore grow on the medium.