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,
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