Bacterial mutagenicity – Ames test

Aim: Detection of gene mutation in a bacterial experimental system.

Background information: Test items showing mutagenic activity are considered to have the potential to be human carcinogens and/or mutagens, this being an important liability for drug development.

The Ames test is part of the battery of genotoxicity tests required by Regulatory Authorities for the evaluation and registration of pharmaceuticals (ICH S2(R1)) and is also the reference assay for the regulatory classification of potential genotoxic impurities (ICH M7(R1)). The assay is based on the exposure to test item of a set of bacterial strains of Salmonella typhimurium and Escherichia coli carrying a mutation that makes them auxotrophic for the essential amino acid histidine and tryptophan, respectively. When exposed to mutagenic agents, these strains revert to a prototrophic condition and leads to an increased number of colonies growing on minimal medium plates.

Experimental procedure

  • Top concentration: 5000 µg/plate, unless limited by solubility/toxicity
  • 48-72 h exposure & expression period; 37ºC
  • Revertants colony counted by automated imagen analysis

Delivered results

  • Bacterial cytotoxicity
  • Absence/presence of mutagenic activity
  • Positive when > 2- or 3-fold increase in revertants (depending on strain)