Ampicillin plates

JG. Head bijgh at
Mon Dec 11 12:08:25 EST 1995

: 	If you still have satelite colonies, you may want to add into 
: your medium Methicillin (an ampicillin derivative antibiotic) at 80 to 
: 100ug/ml final concentration along with your ampicillin.  I'm not quite 
: sure how it cuts down on satelite colony formation so I won't speculate 
: (if anyone knows for sure and have a few minutes to bounce me the answer, 
: I would like to know).

: Hope this helps,

:    ***********************************************************************
:    Michael Gregory Abel    Abel at    423-974-2933 (office)
:    University of Tennessee    Dept. of Microbiology    423-974-4007 (FAX)
:    Knoxville, Tennessee 37996-0845    
:    ***********************************************************************

I can't say for sure about methicillin, because we use carbenicillin, but 
I imagine the principle of satellite colony prevention is similar.  Amp 
resistant cells secrete beta-lactamase into the surrounding media which 
breaks down any Amp present.  This means that if you grow Amp-r colonies 
on an ampicillin plate, after a while the agar surrounding the colony has 
had all its amp broken down, and then non-resistant cells can grow 
forming satellite colonies.  Carb is more resistant to break down by 
beta-lactamases so helps prevent the formation of satellite colonies.  At 
least that is how it was explained to me!

While on the subject - Is methicillin better than carbenicillin?  Has 
anybody used both and formed an opinion?



Jared Head     at the Department of Biochemistry, University of Bristol

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