If no previous agar for recovery calculation may be you have data on workbook or somewhere. If you do not have ability to compare with previous data you need the stock or pellets if reference culture with known number of CFU on it. If you do not have it just make suspension of reference culture and count the quantity of microorganisms by microscopy or use the previous data of dependence of OD from CFU if you have available data.

Hope this info will help you.

Good luck!

thank you Karen ! However we were stuck on regulation requirement that make essential the comparison the tested media and approved one at the same time. This is still an confusing gap if the one wants to builds up a new laboratory. from my point of view, it is impossible to perform first GPT of media in-house.

Karen A. Darbinyan

You can compare two media by performance or grow promotion test.