[Microbiology] Re: Problems with E. Coli

N10 via microbio%40net.bio.net (by limbic_lesion At hotmail.com)
Tue Nov 28 14:05:14 EST 2006

"Nachiket Vaze" <nachi1981 At gmail.com> wrote in message 
news:mailman.192.1164738028.19683.microbio At net.bio.net...
> Hi.
>    I am a grad student in Bioengineering working on a sterlization 
> project.
> 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 plate.
> 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

Hi Nachi

Sounds to me like it is critical that your microbiological data is not only 
comprehensive but accrurate for this project.

As you state  you are not a microbiologist and with respect it does show. 
For example you notes include no mention of measurment of  anaerobes which 
of course  would not show up by aerobic plate count nor any accomodation for 

Additonally the sensitivity of the plate count technique is insufficient to 
really measure efficiency in processes where actual sterility is the goal. 
More sense is obtained by liquid culture of  large masses inorder to 
detrmine the presence of low numbers of survivors.

My recommendation is you either hire a microbiologist or call in the 
temporary services whose skill base and resources  are sufficient for the 
job at hand.

Kind regards  Des 

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