[Histonet] Gram staining

Monfils, Paul PMonfils <@t> Lifespan.org
Thu Jul 21 11:14:38 CDT 2005

I have been making my own gram controls for years. I purchase cultures of
non-pathogenic gram positive and gram negative organisms grown in liquid
suspension (rather than on an agar plate) from a biological supply company.
These are inexpensive, less than $10.00 per culture. When I receive the
tubes I spin them down to concentrate the organisms, remove most of the
supernatant, resuspend the culture in a small volume of its original culture
medium, then inject it into a piece of unfixed lung through a fine gauge
needle. I use lung because there are many small natural spaces to retain the
culture. I push the needle most of the way through the tissue, then slowly
withdraw it as I inject, to distribute the culture through the tissue. Then
inject again perpendicular to the first injection. Drop the tissue into
formalin, fix overnight, process and embed as usual. I embed a gram positive
piece and a gram negative piece side by side in the same block. 

Many different organisms can be used, but I am currently using a mix of
Bacillus subtilis and Micrococcus roseus for the gram positive control; and
a mix of Escherichia coli and Serratia liquefaciens for the gram negative.

I purchase the cultures here:


Click on "living organisms", then "bacteria".

Paul M.

> ----------
> From: 	histonet-bounces <@t> lists.utsouthwestern.edu on behalf of
> jcarpenter764 <@t> aol.com
> Sent: 	Thursday, July 21, 2005 7:42 AM
> To: 	histonet <@t> lists.utsouthwestern.edu
> Subject: 	[Histonet] Gram staining
> Can anyone give me some tips on how to get Gram stain controls or how to
> substitute for the control. Thanks Jennell
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