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Saturday, June 23, 2012

Ames Test : Test for Mutagenicity


Ames Test is the test for detecting chemical compounds which are suspected to be mutagens (Mutagen: agent which causes mutation). Mutagens which induce cancer is known as carcinogen. ames test is for testing the chemical is mutagen or not. Ames test was developed by Bruce Ames, hence the name of the test is known to be Ames Test.

Before developing amest test for mutagenicity, Carcinogentic / Mutagenic testing of chemicals were done by injecting the test chemical (suspected chemical) in mice and analyze for tumors. problem with this method is mutation is low frequency and low levels of mutagenicity goes undetected making insensitive. maintaining large population of mice is a expensive event.

Bruce Ames and co-workers developed a quick inexpensive test for screening mutagenicity of large number of chemical compounds using the bacterial strain Salmonella typhimurium. 


Auxotrophic strain of Salmonella typhimurium is constructed (mutant strain), which require amino acid histidine for its growth, the auxotrophic strain of bacteria would only grow in a medium which is supplemented with histidine.

Ames Test for Mutagenicity


The test is all about the reversion of auxotrophic salmonella typhimurium to prototrophic salmonella typhimurium  (prototrophic starin of bacteria: ability to synthesize all the compounds a parent bacterial strain could synthesize) in the presence of mutagen (suspected chemical compound used for the testing).small amount of histidine is supplemented just to have few cells to grow,  if the auxotrophic bacteria grows in the petri plate containing the test chemical even without supplementing histidine, then that test chemical would be mutagenic and pose threat of inducing mutation.

Certain chemicals which are not mutagenic in its original form but might turn mutagenic when the compound is metabolized, so in the test rat liver enzyme is included so the chemical can be metaboilized and its effect can be analyzed.