Ampicillin bacteriocidal or static?

Henrik Jakobsen hj at
Wed Mar 13 06:05:50 EST 2002

On Tue, 12 Mar 2002 13:34:19 +0000, Michael Witty
<mw132 at> wrote:


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

'Penicillin selection' is a basic technique to isolate auxotrophes.
Say you wan't to select His-minus mutants from a wild type strain.
Grow the strain in liquid minimal media + glucose + penicillin, after
a period of growth add penicillinase to inactivate the penicillin.
Take out a sample and plate it on minimal media + glucose + histidine.

The penicillin will kill all the wild type cells capable of growing in
the liquid media, the His-minus mutants will survive simply because
they do not grow and show up on the plate.

This is of course from E. coli experiments, maybe other bugs have the
sense to stop growing when their cell wall synthesis is affected...

But I still say that penicillin is lethal to growing cells, i.e
bacteriocidal or bacteriolytic.


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