Casella CEL Airborne bacteria sampler User Manual
Page 5
1.
Sterile petri dishes (minimum internal diameter 14cm, maximum
external diameter 16cm), for holding the agar media,
2.
Suitable agar media, for collecting and growing the bacteria,
3.
An Autoclave, for preparing and sterilising the agar media,
4.
A Laminar flow cabinet, for preparing agar plates,
5.
An Incubator, for growing the bacteria on the plates into colonies
after sampling,
6.
Plate counting facilities, for enumerating the colonies after incubation.
In order to minimise the risk of contamination of the sampling media before
and after sampling, standard microbiological practices should be adopted.
3.
PRINCIPLES OF OPERATION
In order to determine the concentration of airborne bacteria, air is drawn into
the sampling unit at a controlled rate, through the air inlet nozzle. The air is
then passed at a high speed through a narrow slit (or slits) located in the
sampling head (which covers the turntable). Two millimetres below the slit
(or slits) a petri dish containing agar is positioned on a turntable and the air
flowing through the slits impinges on the media. Due to the high velocity of
the air and the moist agar surface, airborne micro organisms are captured on
the media. The agar jelly, contained in the petri dish, is then incubated at a
controlled temperature, so that the originally invisible bacteria from the nuclei
of bacterial colonies, become visible to the naked eye and can therefore be
enumerated.
During sampling the petri dish is rotated on the turntable under the slit (or
slits), spreading the bacteria evenly across the surface of the agar to facilitate
the counting of bacterial colonies and to enable the timing of bacteria
deposition to be established.
To achieve satisfactory sampling over a wide range of airborne bacteria
concentrations, a range of air sampling flow rates are available which are
controlled by the number of slits in use and the speed of the pump.
Principles of Operation
Page 5 of 16
BACTERIA SAMPLER
User Manual