Ampicillin bacteriocidal or static?

Michael Witty mw132 at mole.bio.cam.ac.uk
Tue Mar 12 08:34:19 EST 2002


On Tue, 12 Mar 2002, Henrik Jakobsen wrote:

> On 11 Mar 2002 22:59:27 GMT, Johannes Graumann
> <graumann at clyde.caltech.edu> wrote:
>
> >I'm confused and hope someone here might be able to enlighten me. I just read in some
> >medical microbiology book that penicillins and thereby Ampicillin are bacteriocides.
> >This overthrows my whole view on things like the appearance of satellite colonies -
> >how do they show up if not by releaved growth inhibition through Ampicillin by means
> >of beta-lactamase secreted by Amp+ neighbours?
>
> Well, actually penicillins are bacteriolytic. They only inhibit the
> transpeptidation of the cell wall, resulting in a defect/weak cell
> wall. Cell growth will continue as normal until the osmotic pressure
> lyses/kills the cell.
>
> The satellite colonies are merely 'late bloomers' that started growing
> (by pure coincidence) after the Amp-level dropped.

  . . . my microbiology lecturer said that penicillin was bacteriostatic.
I'm not sure what evidence he had.  Mike.




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