Loss of plasmid in liquid culture

Duncan Clark Duncan at genesys.demon.co.uk
Sat Mar 26 08:03:17 EST 1994

In article <Cn4MvH.Mq4 at ncifcrf.gov> pnh at fcsparc6.ncifcrf.gov writes:

> 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.

Maybe I'm wrong. I'd always been led to think that was the case. Whatever the 
mechanism carbenicillin is still better than Amp if somewaht more expensive.


Duncan Clark                        | Internet:    duncan at genesys.demon.co.uk
GeneSys Ltd.                        | Compuserve:  100015.1406 at compuserve.com

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