The Ames test is a bacterial assay used to determine a compound's mutagenicity by testing its capacity to revert mutations present in the tester mutant bacteria and restore its ability to synthesize an essential amino acid required for growth. The following is a simple protocol for the Ames test:

• Isolate mutant strains of His- S. typhimurim.
• Prepare a negative control suspension of His- S. typhimurim in a buffer.
• Prepare a test suspension of His- S. typhimurim in a buffer supplemented with the test chemical and small amounts of histidine.
• Incubate both suspensions at 37°C for 20 minutes.
• Prepare two separate agar plates, pour suspension on two Petri plates, and spread using an L-shaped spreader. Cover the Petri plates with sterile aluminum foil to protect the testing sample from photoreactive substances.
• Incubate plates for 48 hours at 37 °C.
• After incubation, count the number of colonies on each plate.