MediaValidation, GPT test. Criteria?

The question is media validation. (I mean Growth Promotion Test.).

So, all the lots, both manufactured on-site and received outside the company, should be tested for their growth promotion ability.

What should be the criteria?

For some media like TSA, or SDA, for example, we should actually count the CFU and compare.

And that’s where I’m confused, because the USP says “withing 2 folds of standardized inoculum or compared to previously approved lot.”

What criteria should be used? What is standardized inoculum? Or should it be “compared to the previously approved lot?” AGain, if this is the case - what is the criteria of compaison? 2 fold?

But it seems strange to me.
For example, media was inoculated with 98 cfu. The growth promotion test gave 50 cfu. Does it mean that for the next media result of 26 cfu would be OK? Even if we inoculated 98 cfu again? But if that’s the case, for the third lot we check, the result of 14 cfu would be enough to validate :eek::eek::eek:, even if it’s actually about 1/8 of whatever we put into this media!!!

Please, tell me what you use in your companies.

Thank you in advance. Sova.