TA100

TA100 is a strain of Salmonella typhimurium used in the Ames test, a bacterial assay for mutagenicity. It is one of several tester strains (for example, TA98, TA100, TA1535, TA1537, TA1538) designed to detect different types of mutations. TA100 is particularly sensitive to base-pair substitution mutations, which can restore the ability to synthesize histidine when a specific revertant mutation occurs.

The strain carries a defective histidine biosynthesis pathway, requiring histidine supplementation for growth; exposure to mutagens that cause reverse mutations allows colonies to grow on histidine-free medium, enabling quantification of mutagenic potential by counting revertant colonies. Genetically, TA100 contains mutations in the histidine operon and is often maintained with a plasmid element that enhances mutagenesis, increasing assay sensitivity.

In the standard protocol, researchers treat TA100 with a test compound, then plate on minimal medium lacking histidine. Parallel plates with and without S9 liver enzyme mix allow assessment of metabolic activation similar to mammalian metabolism. The number of revertant colonies after exposure is compared to control plates, and results are reported as a mutagenicity index or fold increase.

The TA100 strain is widely used in toxicology and chemical safety testing, providing rapid preliminary screening for mutagenic hazards and is commonly used in both industry and regulatory science. Limitations include differences between bacterial and human metabolism and the possibility of false positives or false negatives, so positive results are typically followed by additional in vitro or in vivo assays.