----- Original Message -----
From: "Hochberg, Alan M" <Hochbeam at Qualicon.email.dupont.com>
To: "Microbiology List Mailing List" <micro-list at qualicon.com>
Sent: Thursday, January 04, 2001 7:34 PM
Subject: Microbiology List: FW: plating efficiency
> From: Florin Amarandei [mailto:amarandi at lhb.tu-darmstadt.de]
> <mailto:[mailto:amarandi at lhb.tu-darmstadt.de]>
> Sent: Thursday, January 04, 2001 11:51 AM
> To: microbio at hgmp.mrc.ac.uk <mailto:microbio at hgmp.mrc.ac.uk>
> Subject: plating efficiency
> Importance: High
>> to determine the plating efficiency is useful to get some information
about
> growth of bacterial cells on solid media. So my questions are:
> What kind of informations can you get from the plating efficiency or in
> other words what does it mean, when the determined plating efficiency is
> only 20 % for example ? In which cases or purposes you have to determine
it
> ? Whoever could answer to these questions should do it. Thank you.
>>A difficult subject,indeed. But the answer depends on what you are looking
at: if you plate the whole bacterial community of, lets say, lake water, you
would have to compare all bacteria present in your sample as counted e.g.
microscopically (after DAPI staining or similar) with the colony count you
get on a specific medium. Plate count will depend on the conditions:
temperature, pH, carbon source, buffer, minerals etc., the total count will
also depend on your method. Plating efficiency will be around 0,5 % to 1
%!!! - with 99 - 99,5 % "non-culturable" or "non-colony-forming" bacteria,
where non-culturable means: under the conditions used.
If you have a pure culture of a culturable bacterium, the situation is much
easier: you count total cells in a light microscope and estimate the
colonies on your plates. Plating efficiency is low e.g. for fastidious
bacteria (e.g. strictly anaerobic, strictly thermophilic, chemoautotrophic
etc.) or after deleterious treatment like protoplastation/regeneration or
electroporation. There it also is a marker of the efficiency of your method.
But with any bacterium - even with the good-natured ones - you will get a
plating efficiency below 100 %: not any cell you see in the light microscope
will be alive or prepared to form a colony. (You could try to stain "active"
cells for counting, e.g. with markers for the number of ribosomes etc. -
then plating eff. should be higher) If you incubate e.g. your E.coli plates
longer, you will find small colonies coming up, you would not count after an
18 hrs incubation.
Wolfgang Schwarz
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