Ask A Scientist© Biology Archive

Question:  I am a teacher seeking information for one of my students who is 
interested in researching lactose intolerance.  She wishes to test bacteria 
(E. coli have been suggested) for intolerance.  Is there a procedure for doing this?
Do you have other suggestions or advice?
This student is a high school sophomore.
Carolyn M McPherson

Answer:  Yes there is a way to find E coli that can't metabolize lactose.
In fact, it's one of the most commonly used methods in
molecular biology.  A colorless chemical (called X-Gal for short)
turns blue if the bacterium can metabolize lactose, and stays clear
otherwise.  SO, if we have X-gal in the agar plate, and streak out the
bacteria, the WHITE colonies are lactose-intolerant!
I don't know for sure, but I will bet that most of the usual supply
houses can provide a kit for this purpose.
Steve J Triezenberg