Ames test: Ethidium bromide

David Micklem dmicklem at cmgm.nospam.invalid
Wed Jul 18 09:33:39 EST 2001

In article < at>, Dr.
James J. Campanella <campanellj at> wrote:

>Let's see:
>Ames test: You mix auxotrophic mutant E. coli with your putative mutagen,
>then you plate the auxotrophic mutant + mutagen on a drop out plate. You
>then sit back and look for wild-type revertants that can grow on the
>drop-out plate. You compare the frequency of revertants on the treated
>plate with a control plate-- the difference between the two is presumably
>the level of mutation induced by your presumptive mutagen.
>Modified Ames test: You do the same as the above, but you include a liver
>extract in your mixture. Many mutagens are activated by enzymes that are
>found in the liver, and so they do not become dangerous until they actually
>get into the body. These mutagens would show up as being non-mutagenic on a
>standard Ames test.
>How was that? Did it make any sense?

Looks good, except that I think its Salmonella typhinurium not E.coli.

I had a quick look in:

McCann J, Choi E, Yamasaki E and Ames B, PNAS (1975), Vol 72, 5153
"Detection of carcinogens as mutagens in the Salmonella/microsome test:
Assay of 300 chemicals" 

(that being the only EtBr mutagenicity reference I could get hold of
easily). [Kudos to Roland Hübner, whose post spurred me to look it up].

EtBr scores as 1012 revertents/5ug ethidium bromide tested, which is
high (assayed in presence of liver homogenate, ie after metabolic

Compare to 18200 revertents/(single cigarette smoke condensate).


Sodium azide: 2240/1ug (assayed without liver homogenate), which I had
no idea was anything other than acutely toxic and explosive. Guess I'll
take more care with it in future (not that I use it often...)

oh and for the person who mentioned caffeine:

<70/6000ug, which counts as non-mutagenic. Maybe things have changed
since 1975.

Take care out there, and watch out for UV-gelbox-burn,


D.R. Micklem,              Time flies like an arrow... 
Dept. of Anatomy,          Fruit flies like a banana.
Cambridge University,      Email:dmicklem at 
Cambridge, UK              Phone: +44 (1223) 333776
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