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Modified Ames Test

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Modified Ames testing is used to analyse potential short term in vitro genotoxicity by using a specific strain of Salmonella typhimurium which has been genetically engineered to preclude the ability for amino acid histidine synthesis.

It can be used as a screening technique to detect the presence of potential dermal carcinogens in virgin base oils used in the formulation of metalworking fluids.


The Ames Salmonella mutagenicity assay is the more widely used short-term in vitro genotoxicity test. The assay employs specific strains of the bacterium Salmonella typhimurium that have been mutated at a genetic loci precluding the biosynthesis of the amino acid histidine which is required for growth and reproduction.

The mutagenicity assay relies upon treating the bacteria with test material over a range of doses immediately below the concentration showing significant toxicity to bacteria. Treated bacteria are then grown on agar plate deficient in histidine. The original mutated Salmonella (histidine-dependent) cannot form visible colonies under such growth conditions, unless they undergo a second mutation and revert back to histidine-independent. After the treatment of the test material, the number of such revertant colonies per agar plate could be used as an indicator of the mutagenic potency of the test material.

In this test method, the MI (the slope of the dose response curve and a measure of mutagenic potency) of a DMSO extract of an oil is compared to the mutagenicity index of a reference oil whose dermal carcinogenicity is known. By correlation, the potential dermal carcinogenicity of the test oil can be assessed. 


  1. “Guideline for testing of chemicals”, Method 471: Genetic Toxicology: Salmonella Typhimurium, Reverse Mutation Assay, OECD, Paris, 1983.
  2. Standard Test Method for Determining Carcinogenic Potential of Virgin Base Oils in Metalworking Fluids, ASTM Designation: E 1687 – 10 (2014).


Approximately 50mL-100mL of sample in a clean amber glass bottle OR clear glass bottle wrapped in foil to avoid exposure to sunlight.


Test Protocols
Method Code Test Description Turnaround Time

Eurofins | ams; TMT - 196100

Modified Ames Test

4 weeks