Competent Cell prep

Imran Fatigue tiredkhan at
Wed Apr 12 22:48:05 EST 2000

In article <Pine.GSO.3.94.1000412093603.8912A-100000 at tin>,
  "Mr. John P Phelan" <jphelan at> wrote:
> Dear All,
> Can anyone assist me here? I have in the last week done several
> cell preps all with great transforming efficiency BUT which also grow
> a control  Amp plate overnight at 37C. I have checked my initial
> which I
> am happy to say is fine. I have disinfected pipettes, autoclaved
> everything, short of doing everything in a level 4 containment I have
> idea what to do.

> Are you always likely to see some background on an Amp control plate?

You should make sure that the ampicillin is fresh. Even if you are
using freshly made up solutions of ampicillin, try to find out how old
the solid ampicillin that you're using is. It's possible that over the
years the ampicillin gets damp and then goes off.

For a couple of years I used a mixture of methicillin and ampicillin to
suppress satellite growth that had become an increasing problem. When
eventually we bought fresh ampicillin, I found that the methicillin was
no longer necessary.

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