Ames test - Principle, Test, Interpretation and conclusion

   Chemical carcinogens can induced mutation which can leads to cancer or tumor. AMES test is uses bacteria for the detection of these potential mutagens which are carcinogenic agents. Ames test is the simple process, it is inexpensive and it is indirect assay for testing of mutagens.

  Ames test is given by Brush Ames in 1970 in university of california. In Ames test becteria Salmonella typhimurium (Histidine auxotroph) is used.

  In this experiment Salmonella typhimurium culture is used, which is an auxotroph for histidine, which means that can not synthesise histidine its own. To grow this organisms you need to provide histidine in medium. 
   Another thing that add into culture is rat liver enzyme so that the test organisms can be metabolised into the metabolites products. 


In Ames test there are two plates are prepared one is test plate and another is control plate.

1). In the Test plate you add a possible mutagen and incubate this plate. Now the bacteria are spread on an agar plate with a small amount of histidine. This small amount of histidine in the growth medium allows the bacteria to grow for an initial time and have the opportunity to mutate. 
  When the histidine is depleted, only bacteria that have mutated to gain the ability to produce their own histidine will survive. After 48 hours of incubation, the mutagenicity of a substance is proportional to the number of colonies observed.
2)  The control plate is without the possible mutagens. Mutation can be random or induced so in a condition where you are not adding a possible mutagens. In that condition also there are chances that the test culture will show you some amount of mutation. That's why control plate is prepared, so that you can check for the presence of natural revertants
  Natural revertants are basically mutants which are having a mutation, which will change their histidine auxotroph back to the wild type form. 

Interpretation :

If the test compound is not mutagenic the number of colonies on the control plate, it will be approximately to the control plate. but if the test compound is mutagenic it will induce a large amount of mutation in the test organisms in the salmonella typhimurium culture and you will obtain a high number of colonies which will indicate a really high number of revertants.

Conclusion :

 If the number of colonies on the test plate is more compared to the control plate in that condition you can conclude that a test compound is actually a mutagen.


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