Positive and Negative Control

Hi,
I'm doing a Total Bacteria test using the pour plate method.
As part of the QA/QC, I will be incubating:
a) the TB agar alone; and
b) the TB agar with the dilution water as a sample.

I will also have a positive and negative control. The positive control will
be a solution containing the dilution water and EColi which will undergo the
same procedure as a normal sample.

As for the negative control, I'm a little confused. Should it be the
incubation of a) TB agar only or should it be b) TB agar with dilution water
as a sample.

As I only want to eliminate the EColi factor, I was thinking of using b) for
the negative control. Is that right?
Thank you for the help.
Rgds
Agatha

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""agy lee"" <[Only registered users see links. ]> wrote in message
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will
the
water
for

(a) will tell you if your agar was sterile to start with. (b) will tell you
if your dilution water was sterile as well and show that your aseptic
technique is adequate.

GS