Germ recovery validation

[Patrick TEULIE]

We are looking for advices on how to validate the germ recovery
on numeration media ready to use from the supplier, such as
Tripcase-soya agar or sabouraud?
According to the PDA's Technical Report #21 the germ recovery has to be
within +/- 30% of the reference.
What can we use as a reference media?
Is there a standard protocol to achieve +/- 30% ?

Thanks for any hints on that matter.

Patrick Teulie