Mold/IAQ Sampling Strategies…Direct Microscopy vs. Culture Technique

by Dr. Rajiv R. Sahay, Pure Air Control Services

The quality of the indoor environment is of increasing concern to everyone, just read your local paper on any given day for articles on “sick” schools, courthouses or homes.  As a result of such media attention and recent epidemiological studies, managing Indoor Environmental Quality (IEQ) has become a critical component of Facilities Maintenance.  But the responsibility of IEQ Management does not end at the maintenance level.  Due to the looming threat of litigation, skyrocketing insurance premiums, and increased health risks, IEQ is a facet of Risk Management, Environmental Health & Safety, and others responsible for the health and comfort of a building’s occupants.

In a perfect world the air we breathe would be free of pathogenic microorganisms, VOC’s and harmful particulates.  A typical indoor environment, however, is not sterile.  The natural tendency of air in the indoor environment to carry microbes coupled with tighter, energy efficient buildings have caused the health risks due to such to grow exponentially. This emphasizes the need for air sampling to monitor our ambient atmosphere.  

Monitoring biological contaminants from the ambient air is not an easy task since airborne 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 aero biota; 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 aero pollutants: the Non-Cultureable, Direct Microscopy Technique and the Cultureable Technique.

1.       Non-Cultureable Direct Microscopy: 

In this technique, specimens can be collected directly from surfaces or from the ambient air.  Surface samples are easily collected using transparent cellotape on microscope slides.  The Bio-Scan 400 (a 2cm digital grid tape imprint), is peeled off, pressed against the contaminated surface to trap the specimen, and then adhered back to the slide.

An ambient air sample can be collected with the aid of a specialized air sampling pump and a slide preparation (i.e. Air-O-Cell Cassette, Micro-5, Burkhard Spore Trap, Cyclex-D, etc…).  Airborne particulates are trapped on gel coated microscope slides within cartridges as air is drawn into them based on principles of impaction due to suction, rotation or gravity.  The slides are then observed under a microscope and the results are tabulated based on the qualitative and quantitative visual examination of the trapped particles.

Advantages of Non-Cultureable Direct Microscopy:

      User friendly – can be easily operated by facilities, risk or safety personnel

      Rapid turn around time – as quickly as 24 hours

      Both qualitative and quantitative estimation of the bioparticulates at a given time and place. Numerical values are provided in cts/cm.

      Cost Effective – Surface Microscopy Preparations with analysis can be obtained from $35.00

      Can give data on other non-viable particulate such as fiberglass, dust, insect biodetritus, pollen, mold, etc…  

Disadvantages of Non-Cultureable Direct Microscopy:

      Efficacy of sampling varies on the type of instrument used.

      Not suitable for very large (i.e. plant trichomes, intact insects, large protozoan cysts) or very small bioparticulate (i.e. viruses and bacteria).

      Viability of the microorganism cannot be determined

      Accurate identification cannot be made after a certain taxonomic level (no speciation).

2.       The Cultureable Technique: 

In this method the airborne particulates are isolated on a culture plate from the ambient air using air samplers (i.e. 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 of the Cultureable Technique:  

      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 of the Cultureable Technique: 

·        Much scientific training is required (e.g. MPH and Ph.D level mycology and bacteriology).

·        Microorganisms are media-specific.

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

·        Microorganisms take time to grow, hence a longer turn-around-time (14 days).

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

·        Expensive - analysis of media plates begins at about $65.00 per plate.  

Which of these two sampling techniques is best to use?  Comparison between the two techniques reveals that the Direct Microscopy Technique coupled with the Culture Technique is the most effective diagnostic tool to assess the severity of a problem potentially caused by microorganisms in the indoor environment. Using both of these techniques also helps to design abatement strategies for controlling problems due to biological aeropollutants in the indoor environment that may affect human health.

Keep in mind, when developing sampling strategies for routine-building assessments (developing baseline conditions) is critical to include both the outdoor air and inside air in the assessment.  This will allow you to compare the inside to outside fungal propagul ratios and determine the similarity of ecological conditions that may affect the quality of indoor air.   

About Pure Air Control Services/EDLab:

Pure Air Control Services provides the following professional IAQ services on a national basis:

      · Pure Air Control Services - multidiscipline team providing forensic IEQ investigations of buildings and homes www.pureaircontrols.com

      · Environmental Diagnostics Laboratory (EDLab) - AIHA accredited microbiology laboratory www.EDLab.org

      · Building Health Check - economical home and building evaluations. Also provides franchise units www.buildinghealthcheck.com

      · IAQ Screen Check Test Kits - do it your self screening of the indoor environment www.indoorairtest.com

      · Building Remediation Sciences - performs remediation on buildings and homes (HVAC system cleaning, mold remediation, chamber cleaning) www.brsciences.com

      · IAQ learning Institute - IAQ Training/Webinars -IAQ training of property management, facility management, risk management, facilities staff..

The parent company, Pure Air Control Services is a certified MBE 8(a) company and is a contractor for the federal U.S. General Services Administration (GSA) Federal Supply schedule (#GSA-10F-0488R). The firm has over 500 million square feet of building/home diagnostics/remediation experience in over 10,000 buildings/homes and has analyzed over 100,000 environmental laboratory samples. In addition, the professional staff has served as expert witnesses in over 100 mold/IAQ-related cases.

Pure Air Control Services state-of-the-art corporate headquarters is located at 4911 Creekside Dr, in Clearwater, Fl serves as distribution point for its IAQ services and products. With satellite offices in Houston, TX, Atlanta, GA, West Palm Beach, FL., Alexandria, VA., Los Angles, CA., the firm services IAQ issues and concerns on a national basis.

For more information, visit the company’s web site at www.pureaircontrols.com or contact Ed Ziegler, VP Business Development at 1-800-422-PURE (7873) ext 804.