Table of Contents
Advertisement
Operations
Adjustable plate holders
The SAS SUPER ISO USB 100 and SAS SUPER ISO USB 180
air samplers are designed for use with standard contact or
Petri dishes.
The plate holders are adjustable to allow for different brands of
plates to be fitted. Adjustable plate holders in the sampler head
allow the operator to use contact plates from various sources.
Colony Forming Unit correction factor
The number of organisms counted on the surface of the dish 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 for both the 55mm standard contact head and the 90mm Petri
head. The probable count (Pr) is then used to calculate the number of CFU per cubic meter
of air sampled.
Example of calculation of results
X=(Pr*1000)/V
Where:
V = Volume of sampled air = 200 litres of air
r (see table) = Colony Forming Units counted on "55 mm Contact Plates"= 67
Pr = Probable count obtained by table positive hole correction = 80
X = Colony Forming Units per 1000 litres (= 1 cubic meter) of air
So:
X=(80*1000)/200 400 CFU per 1000 litres of air (1000 litres=1m
)
3
To express the final result in CFU/ft
multiply the CFU/m
value by 0,02832
3
3
Instruction manual | vwr.com 25
Advertisement
Table of Contents
