Loss of plasmid in liquid culture

[Duncan Clark]

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

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Duncan Clark                        | Internet:    duncan at genesys.demon.co.uk
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