A bacterial reverse mutation test (often simply referred to as an ‘Ames test’) is a core component of safety assessment testing batteries (e.g. ICH S2R1), usually performed in amino acid-requiring strains of Salmonella typhimurium or Escherichia coli. Point mutations, involving substitution, addition or deletion of one or a few DNA base pairs, are detected when they cause restoration of the functional capability of the bacteria to synthesize an essential amino acid. Hence, revertant bacteria are able to grow in the absence of the amino acid required by the parent test strain.
The traditional format of a bacterial reverse mutation test described in OECD Guideline 471 relies on scoring bacterial growth (colonies) on selective agar plates after exposure of the bacterial cells to a test chemical, either by incorporation of the test chemical into the agar plates, or by pre-incubation prior to plating out. This format uses a lot of agar plates and consumes large amounts of test chemical; characteristics that do not easily lend themselves to screening.
A number of ‘cut-down’ Ames tests or alternative format bacterial mutation tests exist, though not all make use of the bacterial strains specifically referred to in OECD Guideline 471. The Gentronix Ames assay, however, uses the recommended OECD Guideline 471 tester strains.
Bacterial Mutation Test at Gentronix
Gentronix currently employs the Ames MPF™ microplate format bacterial mutation test developed by Xenometrix as a component of its testing services. This method utilises small volume, liquid format culturing of the bacterial test strains and a colorimetric read-out for ease of scoring of revertant bacteria after exposure to test chemicals in the absence and presence of metabolic activation using S9 fraction.
Gentronix bacterial mutation testing services provide clients with:
- 384-well microplate format bacterial mutation test
- Colorimetric read-out permits automated scoring (removes subjectivity)
- Low test chemical requirement
- Results from OECD Guideline 471 tester strains