Our website includes a free to use online count correction feature. This will enable MicroBio air sampler users to quickly calculate airborne CFU concentrations and positive hole count correction on visible colony growths in a petri dish or contact plate following microbial air sampling. It is suitable for correcting counts obtained from samples taken using the MicroBio MB1, MB2, MB2-RSH and MB2-HiFlow bioaerosol samplers with any sampling head option. The statistical correction is based upon work published by Macher.
Once a sample has been taken, the contact plate or petri dish should be removed immediately from the MicroBio, the lid replaced on the plate and sealed. A note should be made on the lid regarding time, location and volume sampled. The plate should then be incubated for a period of time and temperature dependant on the requirements of the media. Once incubated, the colony growths are then counted, either manually or using an automatic colony counter.
Why do counts need correcting?
Due to the statistical nature of the sampling method and the chance more than one colony impinged at one point on the dish, count correction needs to be performed. This can be done using the new online count correction calculator, referring to the limited count correction tables in the MicroBio MB1 or MB2 manuals, or if you want to do things by hand, then the correction equations shown below can be used: