Ames test

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  Ames test diagram

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  Ames test mutation example

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  Ames test 384-well plate

The Ames test is a widely used assay to assess the mutagenic potential of chemical compounds. Named after its developer, Bruce Ames, the test is a biological assay that uses bacteria to test whether a given chemical can cause mutations in the DNA of the test organism.

Principle

The Ames test is based on the principle that mutations in the DNA can lead to changes in the phenotype of an organism. In this test, strains of the bacterium Salmonella typhimurium that carry mutations in genes involved in histidine synthesis are used. These strains are unable to grow on a medium lacking histidine unless a mutation occurs that reverses the original mutation, allowing the bacteria to synthesize histidine again.

Procedure

The procedure involves exposing the mutant strains of Salmonella to the chemical being tested. The bacteria are spread on an agar plate that lacks histidine. If the chemical induces mutations, some bacteria will regain the ability to synthesize histidine and form colonies. The number of colonies is compared to a control plate to determine the mutagenic potential of the chemical.

Strains Used

Different strains of Salmonella typhimurium are used in the Ames test, each with specific mutations in the histidine operon. Commonly used strains include TA98, TA100, TA1535, and TA1537, each sensitive to different types of mutations.

S9 Mix

To mimic the metabolic activation of chemicals in the liver, an S9 mix, which contains liver enzymes, is often added to the test. This allows the detection of pro-mutagens, which require metabolic activation to become mutagenic.

Applications

The Ames test is used extensively in the field of genetic toxicology to screen for potential carcinogens. It is a cost-effective and rapid method to identify chemicals that may cause cancer by inducing mutations.

Limitations

While the Ames test is a powerful tool, it has limitations. It uses bacteria, which may not metabolize chemicals in the same way as humans. Therefore, results from the Ames test are often supplemented with additional tests in mammalian cells.

Related pages

• Mutagenesis
• Carcinogen
• Genetic toxicology
• Bruce Ames

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