Carb vs Amp - whats the story?

Paul N Hengen pnh at cockleberry.ncifcrf.gov
Mon Mar 11 17:22:38 EST 1996


John Dixon (jpcd0 at mole.bio.cam.ac.uk) wrote:

: Can anyone fill me in on why/how Carb plates should be better (fewer
: satellites?) than amp ones?

: Is it inactivated more slowly than amp by the bacterial resistance gene or
: something?

This is taken directly from the FAQ list.  If anyone can update this answer
with a better explanation, please let me know...

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37. How do I prevent satellite colonies from appearing on my ampicillin plates?

Satellite or "feeder" colonies appear on ampicillin plates near ampicillin
resistant colonies because the enzyme responsible for antibiotic resistance,
beta-lactamase, is secreted from the cells. The use of other penicillin
derivatives containing beta-lactam rings sometimes alleviates this. It is a
matter of debate whether the enzyme is inhibited from leaving the cell, or the
derivatives are more resistant to the secreted form of the enzyme. In any case,
the number of feeder colonies can be reduced by using 200 ug/ml carbenicillin,
or a mixture of ampicillin 20 ug/ml and methicillin 80 ug/ml.

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Paul N. Hengen, Ph.D. (pnh at ncifcrf.gov)
National Cancer Institute--FCRDC--Frederick, Maryland 21702-1201 USA
phone:(301) 846-5581 fax:(301) 846-5598
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