Question

using the ames test, can you determine if a substance is toxic? If so how?

Answer 1

Yes, to answer your question. However, by toxicity, we mean ability of the substance to mutate the genes of an organism.

It is the biological assay that can determine if a particular chemical can cause mutations in the DNA of the test organism. The test is named after the person who discovered it in 1970, who is Bruce Ames.

In the process we use a biological agent called Salmonella typhimurium, a pathogenic strain of Salmonella, A particular gene of Salmonella is mutated, the gene which is responsible for coding histidine Amino acid is mutated. This type of Salmonella is called as Histidine negative strain. It cannot grow without histidine, as it does not have the ability to produce the amino acid Histidine.

We have the bacterial culture plate with all nutrients except histidine, that means the histidine negative strain cannot grow unless histidine is additionally provided. Now we add the chemical substance to be tested. We observe the bacterial growth after providing adequate conditions for bacterial growth, i.e. a temperature of 37° C and incubate it for 2 days. Now if the chemical is a mutant and converted the histidine negative strain into histidine positive strain.

The above experiment is what happens in vitro (outside the body), to understand how it happens inside the body (in vivo), we need to understand the concept that any chemical ingested in the body is processed by the liver. Hence to test the same, we add liver extract from mice on our culture plate along with other media. Usually the mutagenic properties increases while passing through the liver, hence we are adding the liver extract.

Interpretation of result:

Result 1: There can be no bacterial growth in the plate. Hence the chemical is not a mutant or toxic.

Result 2: There are scattered colonies on the plate. We get to see scattered colonies on the plate. This is due to spontaneous mutation of histidine negative bacteria, not necessarily caused by the chemical. The experiment needs to be repeated 2 to 3 times, to confirm.

Result 3: There are aggregated colonies on the plate. This confirms the chemical is mutagenic. Also the number of aggregated colonies is proportional to the mutagenicity of the chemical.

Result 3 : There are aggregated colonies on the plate. This confirms the chemical is mutagenic. Also the number of aggregated colonies is proportional to the mutagenicity of the chemical.