Alternaria mold spores and hyphae from an indoor surface (C) Daniel Friedman Validity of Indoor Mold Swab Sampling Techniques

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Swab & PCR sampling & tests for mold contamination in buildings: this article explains the use of mold test swabs to collect mold test samples to screen buildings for harmful indoor mold, followed by a discussion of PCR for mold identification and building mold screens. In this article series discuss the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors.

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A Guide to Swab & PCR Sampling to Screen for Toxic Mold in Buildings

15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005

The appropriateness of mold testing at all is discussed here and at MOLD / ENVIRONMENTAL EXPERT, HIRE ? and in other articles at this website. Because mold test validity and mold test accuracy are often confused, readers should also see ACCURACY OF VARIOUS MOLD TEST METHODS. People who need to conduct mold inspection and testing indoors should see MOLD TEST PROCEDURES.

Swab samples can be used to pull particles for microscopic exam but destroy the identifying conidiophores and hyphae; They are more often used to prepare cultures which have the shortcoming cited above. We make use of swabs to sample for bacteriological contamination.

A sterile swab is wiped across a sampled surface, the inserted into a sterile tube for mailing to a lab.
Swabs are processed in one of two ways:

  1. Direct examination: The lab can lift particles from the swab using tape or other methods to make a direct particle examination similar to tape sampling above.
  2. Culturing: The lab rolls the swab across a culture plate to culture the sample for identification.

Shortcomings of swab sampling for mold:

  1. Direct microscopic examination of mold swab samples: determination of species by direct examination is often difficult as the collection method destroys or fails to collect identifying structures such as conidiophores and hyphae. "Rubbing" and possibly even "rolling" the swab on a surface to collect a sample will often destroy key structural components (the conidiophores and hyphal details) which would have been more easily preserved using adhesive tape.
  2. Culturing from mold swab samples (or from mold tape samples): risks misidentification of the dominant species present and may completely miss species which are present due to choice of culture media and growing conditions. See Shortcomings of culturing for details.
  3. Mold test swabs used to collect particles from insulation, fabric, upholstery, carpets, may fail to collect representative material as they only touch surface particles. Vacuuming such surfaces is more representative of what particles are aerosolized by human activity in a building.

Swabs are very effective for use in testing for bacteriological contamination testing but in our opinion they are of less use in fungal work.

A Guide to PCR Methods for Mold Identification

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Polymerase chain reaction (PCR) can be used to identify individual genera/species with good accuracy and fairly quickly. The method requires costly equipment and is not available at most laboratories. Perhaps more important is that the data base of PCR identification information is limited to a small set of species compared with the wide range of genera/species which occur.

At least one excellent national laboratory offers this service for mold speciation. Depending on how rapidly technology drives down the cost and how rapidly the identification data base is expanded, we suspect that this method will see increased use.

The limitations of PCR as a mold identification tool are currently two: first, it is quite costly to perform per sample, and second, it is excellent at identifying the presence or absence of a specific mold you're looking for. It is less useful as a broad spectrum scan expected to pop up with a result of what's present out of the 1.5 million possible candidates - of which only a few are yet even in the PCR database.


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