Ampicillin bacteriocidal or static?

Henrik Jakobsen hj at aub.dk
Tue Mar 12 08:07:17 EST 2002


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.

Henrik




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