Suitability testing & Validations for microbiology - how many replicates?

I would like to know how many replicates are neccessary for verification of the harmonized USP/ EUP methods?
Also is the above verification something that needs to be done for each new formulation?
(In the SOPs @Ankar has on this site the methods are there, but not the determination of suitability or verification of the method.)
Thank you.