“
SAS Super IAQ” Rev. 1 Pg.
19
ENGLISH
4.12. TOTAL BACTERIAL COUNT AND/OR MICRO-ORGANISMS
IDENTIFICATION BY DILUTION
In normal conditions, if sampling is correctly performed, the colonies are easily counted and
collected for identification on the agar surface of the Contact Plate. If very high colony count is
expected, if inhibitors are expected in the air being sampled or if the micro-organisms are to be
incubated at different temperatures, the dilution method should be applied.
The total amount of agar of the Contact Plate is aseptically transferred to a Stomacher bag,
sterile diluent is added and the Stomacher treatment is applied for one minute. The usual
plating technique and/or identification procedures are applied to the processed diluent.
5. FINAL OPERATIONS
Switch off the ON/OFF Main switch (black button).
The unit will switch off automatically after 4 minutes, if the “switchg off option” has not been
disabled for Infrared Remote Control use.
6. CALCULATION OF RESULTS
6.1. Colony Forming Units per 1000 litres of air
The number of organisms counted on the surface of the “Contact Plate” must first be corrected
for the statistical possibility of multiples particles passing through the same hole. The statistical
formula is taken from work by J. Maker. Correction Tables are given below for both the 55
mm standard Contact head, the 84 mm Maxi-Contact head and the Petri head. The probable
count (Pr) is then used to calculate the Colony Forming Unit (CFU) per cubic metre of air
sampled.