You are screening a chemical for potential mutagenicity using the Ames test. You

Question

You are screening a chemical for potential mutagenicity using the Ames test. You used a his – S. typhimurium bacterium for this test and obtained the following results:                     

Control (H2O) ....... Chemical...................... Chemical + rat liver extract   

   19 ............................ 247.................................... 18  

A) Based on these results, do you think this chemical is safe? Why or why not?

B) What was the purpose of also testing water and why did it result in 19 colonies?

Explanation / Answer

AMES test is used to detect the mutagenicity of chemicals. In this test, a mutant strain is taken and treated with a chemical. If the chemical can cause reversions in the mutant phenotype, the chemical is said to be mutagenic.

Given AMES test results:

Water = 19 colonies

Chemical = 19 colonies

Chemical + Rat liver enzymes = 18 colonies

A. From the given results, it appears that the chemical has an inherent mutagenic property. however, the chemical is metabolized to a non-mutagenic substance by the rat liver enzymes. So, it can be used as a safe drug.

B. The water serves as a negative control. It gives the background spontaneous reversion rate. Since water and Chemical + rat liver extract produced an almost same number of colonies, the chemical may be used as a safe drug.

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