agars

John Gentile yjgent at home.com
Thu Jul 5 20:32:43 EST 2001


I've always hated using Ehrlenmeyers for boiling agars. For me the best
flask is a flat bottom round glass flask with a long neck. I brought the
solution to a boil on a stirring hot plate and stopped exactly 1 minute
after boiling. Timing is everything. I would place the melted or autoclaved
agar into a 50 C water bath until I was ready to decant. To pour large
volumes I used a BD glass syringe with a valve attachment and a canula. The
valve was "one way" and had 2 ports - the side port had a tube that went
into the agar flask and the front port had the canula attached. It worked
very well for 1 or 2 liters.

When I had to make XLD agar it was a little different - I used a thermometer
to gauge the melting and didn't let it get over 98 C. Boiling it would
usually cause the bile salts to precipitate out.

Firm agars have 15 gms agar per liter and semisolid agars have 5 gms per
liter. But in either case you have to boil the agar for 1 minute and don't
let it boil over or scorch on the bottom of the flask.

-- 
John Gentile                                    Rhode Island Apple Group
yjgent at home.com                                      President
 "I never make mistakes, I only have unexpected learning opportunities"

> From: Dilworth <bactitech at hortonsbay.com>
> Organization: Infinite Systems - Columbus, OH
> Newsgroups: bionet.microbiology
> Date: Thu, 05 Jul 2001 00:44:08 -0400
> Subject: Re: agars
> 
> Any solution with agar has to boil about a minute before you cool it.
> If it's not totally melted it won't solidify.  Be careful at this stage,
> as it boils over and burns easily.
> 
> I've only ever used premixed plating media with agar already in it, but
> it will turn clear when it's melted.  Use padded gloves and keep
> swirling it periodically while it's heating, unless you melt in an
> autoclave.  We used to make 2-3 liters at a time, so swirling this was
> pretty tricky. If you're using smaller amounts use a large enough flask
> (Ehrlenmeyers are great) so you can swirl, but not too big.
> 
> Good luck.
> 
> Judy Dilworth, M.T. (ASCP)
> Microbiology
> 
> magix wrote:
>> 
>> Hi
>> 
>> I am having trouble with my experiment (water analysis).
>> The method just states "agar" as a solidifying agent and
>> we bought Agar Grade A. Somehow, it won't set.
>> The author of the method recommended Bacto Agar.
>> Is there any difference between these two agars?
>> 
>> If there are so many solidifying agars (which are not selective) then how do
>> you go about choosing the right one for your experiment?
>> 
>> Kei




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