[Microbiology] Re: Problems with E. Coli

Diana Hemdrup via microbio%40net.bio.net (by DIHE At lundbeck.com)
Tue Dec 12 02:51:38 EST 2006

Depending on what it is exactly you are testing, I recommend you use
Bioindicators with eg. Bacillus stearothermophilus or Bacillus subtilis.
Bacillus is gram + and spore-forming. When you need to test for
sterilization you must make use of an aerobic spore-forming bacteria -
as it is the spores that can be difficult to kill ! When the
bioindicators have been exposed to the sterilization you must incubate
them in a liquid substrate containing soy bean or casein for about 3-5
E.coli is not particularly resistant therefore it is not suitable for
sterilization testing. Have a nice day. And good luck on your project.

Best regards
Diana H. 

-----Original Message-----
From: microbio-bounces At oat.bio.indiana.edu
[mailto:microbio-bounces At oat.bio.indiana.edu] On Behalf Of
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Sent: 11-Dec-2006 17:01
To: microbio At magpie.bio.indiana.edu
Subject: [Microbiology] Re: Problems with E. Coli

Nachiket Vaze wrote:
> Hi.
>     I am a grad student in Bioengineering working on a sterlization
> The method that I use for judging the extent of sterlization is the 
> Plate Count method. Since I have NO undergrad background in Micro, I 
> am struggling. I have a few questions to ask, so please bear with me.
> Q1) After one experiment I found 2 types of colonies growing on the
> One was distinct E. Coli like ( round and whitish) The other was like 
> smudge, but with distinct colonies. So I used EMB agar to test them 
> and to my surprise, The smudge colonies gave a green sheen and the E. 
> COli looking colonies did not. How is that possible?
> Q2) Another weird thing is that I had streaked an EMB late from an 
> isolated E. COli colony a few days ago and the plate did show Green 
> sheen but after I taped it and kept it in the fridge for a few days, 
> the sheen disappeared. Is that supposed to happen.
> Q3) My lab is looking at different methods to judge the degree and the

> mechanism of Sterlization i.e. microbial killing. Can anyone suggest 
> something other than Plate Count.
> PLEASE help!!!
> Thanks,
> Nachi
Dear Nachi E.Coli wont be a good indicator for sterilization
testing,since many g+ve spore forming bact. are presant in air.you might
be know one fact is that only 1% of bacteria are culturable in normal
way.colony characters are not used to identify the bact. it is presumbly
understandable.many advance chromatography/ spectroscopy tech. available
to identify the presence of organism on/in objects.

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