Air Sampling: Direct Microscopy Vs. Culture Technique

The quality of the indoor environment is of great concern to the general public. The air which we inhale should be pure and free from microbes, but unfortunately, the air often becomes contaminated in various ways. This air can cause problems to public health. In the past few decades, the health risks due to such cause have grown exponentially. This emphasizes the need for air sampling to monitor our ambient atmosphere.

Monitoring of biological contaminats from the ambient air is not an easy task since these air borne particulates cannot form a well- established community structure as seen on the ground. Therefore it requires professional expertise to isolate, identify and collect other relevant information as to their existence in the ambient air. A number of techniques have been used to understand aerobiota, each of them has their advantages and disadvantages. Selection of the right sampler or technique has paramount importance in assessing the contaminants at a particular site. Presently, two basic techniques of aerobiological investigation are commonly used to analyze bioaeropollutants:

1. Direct Microscopy Technique

In this technique specimen slides are prepared either directly from the source (if known) using transparent cellotape and a microscope slide, or from the ambient air by choosing a specialized air sampler ( i.e. Andersen’s, Rotorot, Burkard’s, etc.). These all work on impaction due to suction, rotation or gravity. Slides are prepared by trapping the particulates of ambient air on a gel coated slide. These slides are observed under a microscope and the results are tabulated based on the qualitative and quantitative visual examination of the trapped particles.

Advantages

· Easy to operate.

· Rapid turn around time.

· Both qualitative and quantitative estimation of the bioparticulates at a given time and place.

Disadvantages

· Efficacy of sampling varies on the type of instrument used.

· Not suitable for very large or very small bioparticulate.

· Viability of the microorganism can not be determined.

· Not suitable for heavily contaminated environments.

· Accurate identification can not be made after a certain taxonomic level (no speciation).

2. Culture Technique

In this method the airborne particulates are isolated on a culture plate from the ambient air using air samplers (Andersen’s, etc.) and are allowed to grow on the media under certain controlled conditions for further analysis. Slides are prepared from growing microorganisms on specific media and are then observed under a microscope for further identification and analysis.

Advantages

· Qualitative and Quantitative estimation of viable aerobiota (to a reasonable degree of approximation) is possible.

· Viability of the isolated aerobiota can be determined.

· Identification of isolated bioparticulates is more specific and accurate (i.e. up to

species levels).

· Biochemical (other analyses) for the various chemicals / toxins etc. of isolated organisms can be done.

Disadvantages

· Much scientific, training is required.

· Microorganisms are media-specific.

· Unable to give data of non-viable particles in the atmosphere.

· Microorganisms takes time to grow, hence time-consuming.

· Antagonism of microorganisms can produce pseudo-identification of biota.

· Expensive

Comparison between these two techniques reveals that the Direct Microscopy technique coupled with the Culture Technique is an effective diagnostic tool to assess the severity of the problem posed by microorganisms in the indoor environment. It also helps to design abatement strategies for controlling problems due to bioaeropollutants in the indoor environment that may affect human health.