Loss of plasmid in liquid culture

Paul N Hengen pnh at fcsparc6.ncifcrf.gov
Wed Mar 23 11:52:29 EST 1994

 In article <764185715snz at genesys.demon.co.uk>
 Duncan at genesys.demon.co.uk writes:

> If you have problems with ampicillin try using carbenicillin or a mixture
> of amp plus methicillin (sorry I don't know the ratio - it is in the 
> Stratagene pCRScript kit). These alternative B-lactams are far more 
> resistant to B-lactamase than amp. This means that your O/N culture stands
. ^^^^^^^^^
> a better chance of being 100% plasmid....

Is this right? I generally use 200 ug/ml carbenicillin, but only use 50-100
ug/ml of ampicillin with high copy number plasmids such as pUC. How then does
antibiotic resistance to carbenicillin occur if not by destruction by the
enzyme?  In an earlier thread on this, it was suggested that carbenicillin
reduces "feeder" (satellite) colonies on solid media due to its interaction at
the cell surface. Rather than what you've said above, ie. resistance to attack
of the lactam structure, carbenicillin may prohibit the excretion of the the
B-lactamase into the media and would therefore not reduce the effective
concentration of antibiotic as would be the case for ampicillin.

* Paul N. Hengen, Ph.D.                           /--------------------------/*
* National Cancer Institute                       |Internet: pnh at ncifcrf.gov |*
* Laboratory of Mathematical Biology              |   Phone: (301) 846-5581  |*
* Frederick Cancer Research and Development Center|     FAX: (301) 846-5598  |*
* Frederick, Maryland 21702-1201 USA              /--------------------------/*

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