Microbiological Analysis of Air

Many sampling devises are available for air sampling. The impingement, bubbling, atomizing, electrostatic membrane filter devices etc. are some of the devices used for collection of air.

The choice rests on the availability, cost, air volume, mobility, sampling efficiency and overall efficacy of the device for sample microorganisms. On the basis of their sampling method, several types of samplers using impingement, centrifugation, filtration and deposition are available.

Depositionis easiest and most cost effective method of sampling. It can be accomplished by merely opening an agar plate and exposing it to air which results in direct impaction, gravity settling and other depositional forces. This has quite low sampling efficiency.

Impingementis the trapping of airborne particles in liquid matrix. Impingement device operates by drawing air through an inlet that is similar in shape to the human nasal passage.

Anderson sampleris multilevel, multi-orifice, cascade sampler which is commonly used in the figure below. The air that is sucked through the sampling port strikes agar plates. Larger particles are collected on the first layer and each successive stage collects smaller and smaller sized particles.

Read Also: Fate and Transport of Micro-organisms in Air

Filtrationis the trapping of airborne particles by size exclusion and deposition is the collection of airborne particles using only naturally occurring deposition forces. Filtration and deposition are widely used for cost and portability reasons. The filtration is used for lipopolysaccharide airborne levels.

Centrifugalsampleruses circular flow patterns to increase the gravitational pull within the sampling device in order to deposit particles (Figure 5.5). The cyclone, a tangential inlet and return flow sampling device is the most common type.

As a result of increased centrifugal forces imposed on particles in the airstream the particles are sedimented out. Liquid medium is used to trap the microbes. Its efficiency is low, but it is inexpensive, easily sterilised and portable. Traditionally, culturable and microscopic methods have been used.

Now immunoassay method is used extensively in biomedical research for bioaerosol analysis. Fluorescence immunoassay and radioimmunoassay are used for allergens such as dust mite allergen and animal dander. Biochemical assays are used to measure endotoxins or mycotoxins.

Microbiological Analysis of Air
Fig.: Anderson Sampler. Source: Anuradha S. Nrurkar, 2006

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Benadine Nonye

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