Removing disinfectants, Skc limited warranty and return policy – SKC 225-95 Series Gelatin Filters User Manual
Page 4
Indirect Method
Dissolving Gelatin Filters Aft er Sampling Airborne Microbes
This method is used to prevent osmotic shock to
the sampled organisms, to provide sub-samples for
removal of inhibitors such as disinfectants, for dilution
of the sample where high counts are expected, or to
allow plating onto diff erent nutrient media where
species identifi cation is required.
1. Dissolve the gelatin fi lter in sterile liquid warmed
to 35 to 40 C, such as physiological saline or 0.1%
peptone water.
2. Stir the solution using a sterile magnetic stirrer to
accelerate fi lter dissolution.
3. Process the solution according to Koch’s pour plate
method or the membrane fi ltration technique.
4. Incubate samples.
5. Evaluate colonies that form.
Note: During the dissolving and stirring process (indirect method), the colony-forming
units are separated into individual microbes so you will obtain a higher CFU count than
with directly placing the exposed fi lter on a culture medium (direct method).
Calculation of Colony-forming Units per m
3
To determine the quantity of colony-forming units per cubic meter of air (CFU/
m
3
), compare the number of colonies in relation to the volume of air originally
sampled.
Removing Disinfectants
Note: It is strongly recommended that you use the indirect method when analyzing
samples from an area sprayed with disinfectants or where antibiotic airborne particles are
present. Using this method allows the removal of the disinfectants that inhibit the growth
of microbes on the culture medium. Follow this procedure:
1. Dissolve the gelatin fi lter as instructed above.
2. Before Step 3, fi lter the resulting liquid through a 0.45-μm pore size
membrane fi lter.
3. Add sterile water to rinse the fi lter.
SKC Limited Warranty and Return Policy
SKC products are subject to the SKC Limited Warranty and Return Policy, which
provides SKC’s sole liability and the buyer’s exclusive remedy. To view the com-
Form 40060 Rev 1201
Indirect Method
Sample
Dissolve gelatin in sterile
solution
Filter solution through
membrane fi lter
Filter to agar
Incubate
Count