Positive and Negative Control

Graham Shepherd muhero.nospam at globalnet.co.uk
Thu Dec 18 14:39:49 EST 2003


""agy lee"" <agyleesy at hotmail.com> wrote in message
news:Law12-F98VfdY6hlHK90004eefa at hotmail.com...
> 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
>

(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





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