Ames test for bacterial mutagens

McMahon RE, Cline JC, Thompson CZ. 1979. Assay of 855 test chemicals in ten tester strains using a new modification of the Ames test for bacterial mutagens. Cancer Res 39 682-693. 

The biocompatibility of these amines is good. No mutagenic or cytotoxic effects have been observed for pure DMAPAA or DMAG using the Ames test for bacterial mutagenicity and the agar overlay test for cytotoxicity (33). 

Muta-Chromoplate is a modified version of the classical Ames test for the evaluation of mutagenicity. The bioassay uses a mutant strain of S. typhimurium. The reverse mutation is recorded as absence of bacterial growth after 5 days incubation [55]. 

Ecoflex (powder) was tested for its mutagenic potential on the basis of its ability to induce point mutations in several bacterial strains Salmonella typhimurium and Escherichia coll) in a reverse mutation assay (Ames test), according to OECD guideline 471. Results revealed that the polyester is not mutagenic to bacteria. 

Almost all bacterial mutagenicity tests for carbon tetrachloride have been negative. Ames tests for reverse mutations using several strains of Salmonella typhimurium, with and without metabolic activation, were mostly negative. A weakly positive geno-toxic response was reported in yeast. Negative or weak responses were observed in four studies examining unscheduled DNA synthesis. 

The Ames test involves the reversion from a his— to his+ phenotype in any one of multiple bacterial strains (usually five strains are tested simultaneously). If the addition of test compound to a his— strain of bacteria allows them to grow on histidine deficient media, the obvious conclusion is compound-induced mutagenesis and a high potential hazard for the compound being carcinogenic. This test can also be conducted in the presence or absence of metabolic activation, in order to provide more information on potential risks (i.e., the parent compound may not be mutagenic, but the primary metabolite may present a safety risk). In practice, a positive Ames test almost always leads to discontinuing work on a compound of interest, and so these data are always collected prior to nomination of a compound for development. 

A variety of methods are available to test a chemical for mutagenicity, i.e., its effect on the genetic material. The Ames Test has gained most recognition as a shortterm test [23],This is a bacterial test which allows fast performance and requires limited expense. Its correlation with the mutagenicity of mammals or even with a carcinogenic effect on mammals or humans has repeatedly been tested [24], but remains controversial. 

Professor Bruce Ames, a biochemist at the University of California at Berkeley is one of the pioneers of this type of short-term testing. The Ames Test, as it is called, is now widely used, typically as one of several short-term tests that constitute a series of tests, or battery. A battery is thought necessary because no single test is adequate to detect all types of genotoxicity. The Ames Test involves the use of mutant strains of a common bacterium. Salmonella typhimurium, that back-mutate to their normal state in the presence of a mutagenic chemical or metabolite. Many other bacterial and mammalian cell systems have been made available for this type of testing. 

Before administration of a NME to man, a mutagenicity test in bacterial cells (Ames test), with and without metabolic activation, and tests for chromosomal aberrations in mammalian cells should be negative. Any positive or equivocal results will require additional tests to be performed before proceeding to man. Studies of embryo-foetal toxicity should be performed before administration of a NME to women of reproductive potential. Studies of fertility, early embryonic development and pre- and post-natal development are not required at this stage of development neither are carcinogenicity studies. 

Bacterial Toxicity. A variety of criteria are used by testing laboratories to determine toxicity during the Ames test and when additional sample preparation (i.e., fractionation) is required to separate toxic components from potential mutagenic components of a complex mixture. However, no uniform criteria are available or accepted. The following criteria were proposed and accepted by panel meeting participants as the appropriate conceptual basis for determining lack of... 

Since the respiration of bacterial cells is directly and immediately converted to an electric signal, the preliminary screening of mutagens is possible within 1 h. Moreover, the microbial sensor system employs a homogeneous suspension. Consequently, the sensitivity of the microbial sensor is higher than the "rec-assay". The minimum measurable mutagen concentration is 1.6 jg ml-1 by the microbial sensor and 5.0 /jg ml"1 by the "rec-assay" and 10 p.g ml"1 by the Ames test (26) for AF 2. 

Some dyes exhibit a mutagenic potential. The Ames test is commonly used as a first screening for the prediction of mutagenicity of a substance. It is a bacterial point mutation test inducing activity, which uses special strains of the bacteria Salmonella typhimurium with growth-dependence on the amino acid histidine. The dose-dependent reversion to histidine-independent growth is the marker for a point mutation. 

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