pharmaceutical microbiology

hi
i dont know how can i apply the formula in the usp in chapter <1227> validation of microbial count
http://www.pharmacopeia.cn/v29240/usp29nf24s0_c1227.html

thanks.

I'm not sure what you mean but doesnt the formula just involve you plating different dilutions of your sample and ensuring that your 10X dilution has 10X the amount of bugs on it thus validating your plating technique and ability to accurately measure the number of bugs present?

We validate colony forming units by plating serial 10-fold dilutions of our cultures. In order to save plates, you can do the dilutions in 96 well plates, and then plate 25 ul drops from each dilutions - multiple drops per agar plate. Find the drops that have about 50-150 colonies and count the colonies per drop. Multiply this by the dilution factor, and then by 40 to determine cfu/ml. You can confirm your dilutions by counting drops one dilution higher or lower and making sure there is about a 10 fold difference.