Advice on test results (microbiological challenge test) - (Aug/27/2015 )

Hi everyone,

I need a bit of advice on the results I have obtained from my experiment.

So I conducted a microbiological challenge test also called PET/AET. 

What i have observed is that there are no log reductions but the bacterial colonies (cfu/ml per plate) have still reduced. The log reductions are like 0.7 or 0.1, or 0.3 which is basically nothing.

Thus i am having hard time analysing results as I do not know whether the preservative system/product in question can be passed off as an effective antimicrobial or not

So how can this be possible ?   has anyone else experienced this too  

Assume USP <51> or similar protocol.  Not sure why you would expect the result to be otherwise, but +/- 0.5 log is considered normal plate count variability in such tests. It sure doesnlt appear to be effetive.   What is your preservatve system and in what product category?