TA97a and other Ames tester strains, S. typhimurium and E. coli strains, have been used for more than 40 years to detect mutagenic compounds in chemicals, pharmaceuticals, copsmetics, biocides, water and other environmental samples. They are all listed in the guideline OECD 471:Bacterial Reverse Mutation Test and in guideline ICH M7 for genotoxic impurities. Point mutations were made in the histidine (Salmonella typhimurium) or the tryptophan (Escherichia coli) operon, rendering the bacteria incapable of producing the corresponding amino acid. These mutations result in his- or trp- organisms that cannot grow unless histidine or tryptophan is supplied.
A test sample's mutagenic potential is assessed by exposing these amino acid-requiring organisms to varying concentrations of sample and selecting for the reversion event. Media lacking histidine or tryptophan are used for this selection which allow only those cells that have undergone the reversion to histidine / tryptophan prototrophy to survive and grow. A mutagenic event causing base substitutions or frameshift mutations within the gene may cause a reversion to amino acid prototrophy. These reverted bacteria will then grow in histidine- or tryptophan-deficient media, respectively, whereas non reverted bacteria will not be able to grow. The media during the growth phase can be liquid or agar based.
TA97a strains are used in agar based Ames Test, in minitaturized agar based (MicroAmes24, NanoAmes™) and liquid format Ames Test (Ames MPF). The strains are used in accordance with Guidelines OECD471, ICH M7, ISO 11350:2012.
Characteristics
Safety
In most countries the Ames S.typhimurium tester strains are categorized under the biosafety level 1 (Risk Group 1, Biological agents that are unlikely to cause human disease). Please contact your local authorities to verify biosafety level in your own country.
The host cell Salmonella typhimurium used in the Ames test system does not contain any genes from other organisms except for the species Salmonella typhimurium and is considered non-GMO. Exception is TA102. The mutations in the different Salmonella typhimurium strains were obtained by in vitro recombination within the species Salmonella typhimurium. The TA strains have a significantly reduced lipopolysaccharide layer and are not pathogenic. The plasmid pKM101 does not contain any external genes. It derives from the plasmid R46. The strains do not disturb the biological diversity. The same accounts for the host cell of Escherichia coli used in the Ames test system.
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