USP Preservative Effectiveness Test Questions

I'm new in a pharmaceutical company--in early training to take over the USP
Preservative Effectiveness Testing. So I'm researching this on my own and 
have a few questions:

1. By the USP, at T-zero, product is inoculated 0.1ml containing 10-to-the-
5th to 10-to-the-sixth microorganisms. 
On the same day, that inoculated product is diluted and plated. How do I 
determine the appropriate dilution of the inoculated product at this point?  
(i.e. on T-zero, do you always plate 10-to-the-4th and 10-to-the-5th--
making two 1/100 dilutions and plating 1ml and 0.1ml? 

2. At T-7,14, 21, how do you determine the appropriate dilution of the 
inoculated product? 

Also please suggest any pharmaceutical newsgroups.

Thank you,
Gaia213