DNA Mold Testing

What is the best way to use QPCR for environmental mold testing?-Anon

            There are different approaches for using QPCR for mold testing.  These include the identification of mold species in bulk samples, the identification and quantification of mold species collected in air sampling and, conducting an Environmental Relative Moldiness Index (ERMI) assessment.

            Bulk samples are often collected from materials that are obviously infested (ceiling tiles, gypsum board, carpeting, etc.) or suspected to be infested (wet ceiling tile, carpet, wet spray-applied cellulose insulation).  The advantage of using QPCR in this instance is that one can both easily identify and quantify major mold types present.  The author has used this to characterize and quantify the extent of mold infestation of wet spray-applied cellulose insulation (WSACI) in a research study that has been recently published (reprints are available upon request)

            QPCR has also been commonly used to identify and quantify mold types collected as a result of air sampling.  Air sampling in such cases generally includes relative low sample flow rates (~ 3-4 L/min) and extended sampling times (several hours minimum; up to 24 hours desirable).

            Air samples can be analyzed based on sampling objectives and costs.  Laboratories offer four or more analyses panels(Mycometrics)  These may include a relatively low cost panel of four mold species (Aspergillus versicolor, A. niger, Penicillium chrysogenium, Stachybotrys chartarum) that are indicators of indoor mold contamination.  A second panel includes a total of 8 signature species associated with water-damaged environments (additional species include Acremonium strictum, Memnoniella echinata, Ulocladium botrydis and P. brevicompactum/stolonifera).  A third and somewhat more expansive analysis panel includes a total of 15 species commonly found indoors (these include 4 additional species of both Aspergillus and Penicillium as well as Chaetomium globsum.  The most commonly used analyses panel includes 23 total species.  This panel includes additional members of the genera Aspergillus and Penicillium as well as Alternaria alternata, Paecilomyces variotii, Scopulariopsi brevicaulis/fusca, and Trichoderma  harzianum.

            It must be noted that the analysis cost (from about $100-250/sample) for QPCR samples are much higher than those for spore trap sampling ($25-60 per sample).  These analysis costs must, however, be placed into context with the quality of the results obtained.  As I have written previously, the results of spore trap analyses reported by many laboratories do not accurately quantify mold spores present in a sample and they cannot accurately identify and quantify spores of the genera Aspergillus and Penicillium some of the most important fungal species found in indoor environments.

            The bottom line is that consumers of mold testing services usually buy an inferior product.  Most spore trap results reported by commercial laboratories cannot be reliably interpreted.  As a result, they are of little value in determining whether an indoor air mold contamination and exposure problem exists in a building.

 

 

To be continued

 

March 31, 2007