mstanbro at bih.harvard.edu
mstanbro at bih.harvard.edu
Tue Mar 18 12:12:36 EST 1997
In article <e-anderson-1403970958580001 at news.ski.mskcc.org>,
e-anderson at ski.mskcc.org (eric anderson) wrote:
> > >We're using an ampicillin based expression system but may be having
> > >trouble with scale-up due to ampicillin depletion. My boss remembers
> > >seeing an lactamase resistant analog of ampicillin compatable with
> > >our AmpR vector. Can anyone provide a refference to such an
> > >antibiotic?
> > I don't actually have a reference but...
> > You are probably refering to carbenicillin which is chemically
> > more stable than ampicillin (?less protein reactive). It is, of course,
> > *not* resistant to beta-lactamase (as otherwise it would kill ampR
> > bacteria) but lasts longer in agar plates and in liquid cultures.
> > The downside is that it is considerably more expensive than ampicillin.
> > Another alternative is a mixture of ampicillin + methicillin.
> > Bernard
> the downside of Amp+Meth is that Methicillin is no longer available from
> Sigma, Fluka or Calbiochem (all places where we have gotten it in the
> past). if anyone still knows of a source of Methicillin i'd love to hear
> about it. we've got 25g still but that won't last forever.
Methicillin falls into a small group of semi-synthetic penicillins which
are used to treat S. aureus infections because they were originally
resistant to staphyloccal penicillinases. Many staphyloccal strains are now
methicillin-resistant, which generally means the strain is no longer
sensitive to any of the penicllinase-resistant penicllins and to the
cephalosporins. Methicillin is no longer used in the medical community, at
least in Boston, and this probably explains its scarcity -- it is no longer
The current replacement for methicillin, nafcillin, is available from
Sigma. It could probably be used as a methicillin replacement, although I
haven't used it and haven't seen it in the literature. The sources I have
read indicate these penicillins are not effective against gram-negative
bacteria in human therapy. Whether this is true at the concentrations used
on plates may be another story. Peak serum concentrations for penicillins
after oral administration are on the order of 1 - 10 micrograms per ml. I
don't know if a 10-fold increase in concentration of methicillin or
nafcillin would cause killing of gram-negatives. It may be that methicillin
spared ampicillin by acting as a beta-lactamase inhibitor in meth + amp
plates, and didn't actually contribute to killing per se.
The cost of one gram of penicllinase-resistant penicillins available from
Sigma are: nafcillin - $21.25, oxacillin - $14.75, cloxacillin - $18.90,
and dicloxacillin - $18.35. You might do considerably better if you are
affiliated with a hospital. The price per gram vial of nafcillin at the
hospital at which I work is about $2.
I hope this helps.
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