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December 2003

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Subject:
From:
Brenda Cantillon <[log in to unmask]>
Reply To:
The Pharmaceutical Microbiology Forum Email List <[log in to unmask]>
Date:
Mon, 8 Dec 2003 12:02:10 +0000
Content-Type:
text/plain
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I have a question for the group about reporting total aerobic count results
for samples tested by membrane filtration.

The procedure is as follows:  (ref Ph. Eur. 2.6.12)
For  total  viable count (non-sterile product) a 10g sample is dissolved in
buffer  and  membrane  filtered  onto  2  plates  e.g.  each  plate  volume
represents 5g of product.  The total count between the 2 plates is quoted -
not an average.

Typically  even  counts are obtained on plates e.g. 4 on one plate and 5 on
the  other....  However, recently we saw an unusual variation of a count of
28 CFU on one plate and 7 CFU on another plate, and also 8 CFU on one plate
and none on the other for a different sample?
Is this just typical of uneven distribution of m/os in the sample?
Does it look like analyst error? Should the result be invalidated?
Should we have a limit of variation of counts between 2 plates?

thanks and regards,
Brenda

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