An interesting essay has been published on-line about Colony counting by R. Hutchinson:

Plate counts of colony forming units (CFUs) are the gold standard of microbial enumeration and therefore essential to environmental monitoring in the pharmaceutical industry. There are strict regulations regarding bioburden at each stage of pharma production, from raw materials to finished products, but we often fail to question whether current methods are rigorous enough to fulfil these requirements.

The article can be accessed here.

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology