Chroma Class 102

R.A. Mateer, R.A. Beck

The potential for genotoxicity has been historically assessed on the basis of the Ames test.

The Ames test relies on a bacterial probe embodied as a definitive and consistent strain of Salmonella typhimurium. The S. typhimurium is typically unable to synthesize the amino acid histidine and it is accordingly designated as histidine negative (His Ð). When the bacteria experiences an insult to its genome, it may result in the detectable ability to produce histidine and it is accordingly said to be histidine positive (His +).

The phenotypic expression for the ability to produce histidine and become His + is interpreted as evidence that a chemical agent or some other factor created an insult to the genome resulting in a detectable alteration of the DNA or DNA expression. Statistical studies of occurrence frequencies for His + responses under different concentrations of mutagenic or genotoxic substances, or in response to doses of radiation may be carried out to assess genotoxic or mutagenic potentials.

The Ames test has been the benchmark standard for assessing mutagenicity and genotoxicity but it is expensive and time consuming. This has spurred the development and search for more expedient protocols that give similar results to those ordinarily obtained from the Ames test.

In particular, bioluminescent testing (BLT) can offer cost advantages and speed over the Ames test. Unlike the Ames test, BLT uses dark mutants of Photobacterium phosphoreum M169 (Vibrio fischeri) that have lost their ability to produce luciferase-mediated luminescence. This loss of bioluminescence is probably due in part to repression of the bacterial luinescence operon. Thus, a positive BLT for genotoxic or mutagenic compounds results from an increased reversion rate responses that make the bacteria discharge higher levels of luminescence. The levels of luminescence can be quantified and thereby potential genotoxicity or mutagenicity responses may be correlated to concentration of a specific substance.

Applications for Mutatox Testing

Applications for this type of testing are as varied as the basic problem of genotoxicity.

Many industries have queries about the genotoxic status of certain chemicals in their plants so as to ensure worker safety and occupational safety issues.

  • Hazards Analysis at Critical Control Point (HACCP) programs benefit from oversight of genotoxic substances if there is a chance that toxic or dangerous materials may breach the security of a manufacturing facility.
  • Environmental contamination and toxicology problems often require some index of potential toxicity and genotoxicity before addressing more detailed and comprehensive problems.
  • Construction industries can benefit from Mutatox testing in cases where unknown materials are uncovered in excavations and little is known about the nature or potential toxicity of an apparent waste cache.
  • The Department of Defense and the Environmental Protection Agency have used the Mutatox test for assessing the toxicity of benthic sediments for toxins and ammunition waste products in well documented reports. The uses are so wide and varied for applications of this genotoxicity test, yet it remains quite unknown to industry sectors and government agencies that could benefit the most.

Principals at Chromaceutical were the first to apply the technology to routine analysis of foods in a parallel study with the Ames test in the last major food irradiation study conducted by the U. S. government to eliminate hemorrhagic Escherichia coli 0157:H7 from the meat supply. The results for both test results were found to be comparable. The test also finds utility for assessing the genotoxic potential of new organic compounds as well as studies where medical devices may come into intimate contact with tissues. Sometimes where least expected, substances will give a positive genotoxic response such as in the case of latex used for any number of applications including rubber gloves, tubing and so on.

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