N. 54 - Application of MPN in microbial air environmental tests

When the air is aspirated through the aspirating head of the air samplers indicated in the USP 1116 (Slit to agar samplers, Sieve impactors, Centrifugal samplers, Surface Air System) and micro-organisms impact upon the agar surface there is a statistical probability that the micro-organisms may land on top of each other and be visually interpreted as one single colony (CFU).