What does the Ames test screen for?

• A. A bacterial reverse mutation assay that screens for mutagenic potential by measuring revertant colonies.
• B. A mammalian cell assay that measures cytotoxicity.
• C. An in vivo test of organ toxicity in rodents.
• D. A test for protein binding affinity.

Answer: (A)

The main idea is to detect whether a chemical can cause genetic mutations. The Ames test uses bacteria that cannot grow without histidine, so they require a mutation to become histidine-independent. If the tested compound induces such mutations, colonies will appear on histidine-free plates, and the number of these revertant colonies reflects the mutagenic potential. Often a metabolic activation system (like a liver enzyme mix) is added so the test can identify pro-mutagens that become mutagens after metabolism. Different bacterial strains help catch different mutation types, such as base-pair substitutions or frameshifts. This makes the test a handy early screen for mutagenicity and potential carcinogenic risk, rather than a cytotoxicity test, an in vivo toxicity study, or a protein-binding assay.