Use this calculator to determine 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 microbial air samples taken using the MicroBio MB1, MB2 and MB2-RSH bioaerosol samplers with any sampling head option.
How are the results calculated?
Based upon work published (2688387) the positive-hole correction count is calculated using:
Where Nh is the number of holes on the sampling head, Nf is the number of counted colonies and Nc is the corrected count.
If the counted colonies, (Nf) exceeds the number of sampling head holes (Nh), then the mathematics will fail and the results cannot be trusted. If this is the case, then the sample dish can be considered as overloaded with organisms and the user should consider lower sampling volumes.
The colony concentration is calculated as the corrected count per volume of air sampled. The results are normally expressed in colony forming units per cubic metre. To convert the corrected count to CFU/cu.m use the equation
Where Nc is the corrected number of colonies counted and Vs is the sampled volume in litres.
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