The Ames Test or Bacterial Reverse Mutation Test

BACKGROUND:

The Ames test is a commonly used method that utilizes bacteria to test whether a particular chemical can cause mutations in the DNA of the test organism. It is a biological assay that is formally used to assess the mutagenic potential of chemical compounds. A positive result from the test will indicates that the chemical is mutagenic and therefore may act as a carcinogen, as cancer is often linked to mutation.

The test also serves as a quick and convenient assay to estimate the carcinogenic potential of a compound because standard carcinogen assays on mice and rats are time-consuming (taking two to three years to complete) and expensive. Although it is also noted that false-positives and false-negatives are known.

The Ames testing is also used to test water extracts from plumbing products in contact with drinking water, using Salmonella typhimurium histidine (His) reversion system, which involves mutation of the histidine locus in the genome of several strains. This test is conducted in compliance with Organization for Economic Cooperation and Development (OECD) 471 Guideline for Testing of Chemicals: Bacterial Reverse Mutation Test.

Abbreviated assays are available for certain situations, for example the modified Ames Oil test and Mutagenic Activity of Water Extract test ( AS/NZS 4020).
 

PRINCIPLE OF TEST:

This test is based on the principle of reverse mutation or back mutation. So, the test is also known as bacterial reverse mutation assay.

• Test organism: Ames test uses several strains of bacteria (Salmonella, E.coli) that carry mutation. Eg A particular strain of Salmonella Typhimurium carry mutation in gene that encodes histidine. So it is an auxotrophic mutant which loss the ability to synthesize histidine (an amino acid) utilizing the ingredients of culture media. Those strains are known as His- and require histidine in growth media.
• Culturing His- salmonella is in a media containing certain chemicals, causes mutation in histidine encoding gene, such that they regain the ability to synthesize histidine (His+) This is the reverse mutation. Such chemicals responsible to revert the mutation is actually a mutagen. So, this Ames test is used to test mutagenic ability of varieties of chemicals.

Above content on Principle of The Ames Test and image are references from www.onlinebiologynotes.com  

For routine mutagenicity testing, the Salmonella tester strains recommended are TA97a, TA98, TA100, TA102 and TA1535.TA1535 is optional, and TA1537 is replaced by TA97a.

METHOD REFERENCE:

1. Method 471: OECD Guideline for testing of Chemicals, Bacterial Reverse mutation Test, OECD, Paris, 1997.

SAMPLE REQUIREMENTS:

If sample is in liquid form, minimum of 10mL will be required. Otherwise, sample requirement depends on the physical form of the product, i.e. Tablet, Bone implants etc.  Please contact us to discuss about this.

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