MICROBIOLOGY (Air Sampling Methods) EXAM STUDY GUIDE LATEST UPDATED WITH VERIFIED SOLUTIONS RATED A.
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AIR SAMPLING METHODS
Methods of Air Sampling
The various methods of air sampling include:
1. Impingement which is trapping of airborne particles in a liquid matrix.
2. Impaction which is forced deposition of airborne particles on a solid surface.
3. Centrifugation which is mechanically forced deposition of airborne particles using inertial
forces of gravity.
4. Filtration which is trapping of airborne particles by size exclusion.
5. Deposition which is collection of airborne particles using only naturally occurring
deposition process.
The two most commonly used devices for microbial air sampling are all glass AGI-30
impinger and Anderson 6-stage impaction sampler. Apart from these, the Reuter air sampler
(based on centrifugation) is also commonly used for small scale air sampling.
Impingement
Impingement into Liquid – Impingement in liquids:
In this method, the air is drawn through a very small opening or a capillary tube and bubbled
through the liquid. The organisms get trapped in the liquid medium. Aliquots of the liquid are
then plated to determine its microbial content. Aliquots of the broth are then plated to
determine microbial content e.g. Bead-bubbler device
Impingement on to Liquid is divided into three types, they are following:
(i) Raised Impinger
(ii) Bead- Buffer Device
(iii) Lemon Sampler
Raised Impinger - In this type of sampler impingement is made within bulk fluid by a jet of
air.
Bead Bubbler Device -It is also an oldest device for sampling air. It consists of a 250ml
suction flask which has an outlet on the side connected to suction pump. A glass bubbler,
which is nothing but a glass tube with minute openings at the bottom, is kept in place inside
the flask by a rubber stopper. Glass beads of size about 5mm in diameter are kept around
the glass bubbler.
In addition the flask contains known volume of broth. Air is drawn into the flask through the
glass bubbler when the flask is continuously shaken. The incoming air escapes into the broth
in the form of bubbles through the holes at the bottom of glass bubbler.