Indoor sampling for airborne mould spores may be conducted to help in evaluating occupants ill health complaints, determining the effectiveness of remediation procedures, or assessing health hazards or proactive indoor air quality monitoring. Mould spores enter a building from outdoors through:
- air intakes for the heating, ventilation, and/or air conditioning system (HVAC),
- doors and windows
- contaminated building materials and contents.
The common practice in mould investigation is therefore to compare indoor airborne fungal populations and their concentration to those of outdoor samples. While this can work fairly well for culturable air samples if the moulds have been correctly identified to species, it may not work all the time for non-viable samples. This is particularly the case when the samples are dominated by spores reported as Aspergillus/Penicillium, unidentified spores, basidiospores, or ascospores.
Key Points To Remember When Comparing Indoor/Outdoor Concentrations of Aspergillus/Penicillium and Unidentified Spores
Spores of Aspergillus and Penicillium are rounded or slightly elongated, and smooth or ornamented depending on the species. Since these spores have no other distinguishing characteristics, laboratories usually lump them together as Aspergillus/Penicillium when they analyze air by direct microscopy (total spore counts).
Unfortunately, there are many other genera and species which produce spores that are very similar and difficult to differentiate from Aspergillus and Penicillium. For example, spores of some mould species belonging to the following groups may be misidentified as Aspergillus/Penicillium: Trichoderma, Absidia, Acremonium, Aphanocladium, Beauveria, Chromelosporium, Cladosporium, Phialophora, Gliocladium, Metarrhizium, Monocillium, Mortierella, Mucor, Paecilomyces, Syncephalastrum, Verticillium and many others. Fortunately most of these are not as common indoors as the Aspergillus and Penicillium species.
Labs usually do not indicate whether all the unidentified spores including unidentified ascospores and basidiospores belong to the same group or not. This means that trying to compare indoor/outdoor counts of these categories of spores could be erroneous since one could be comparing spores belonging to totally different genera.
Where significant numbers of Aspergillus/Penicillium and unidentified spores (including ascospores and basidiospores) are involved, culturable air samples may be taken. This would help in characterizing most of these moulds if they produce spores in culture.
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- Brian G. Shelton, Kimberly H. Kirkland, W. Dana Flanders, and George K. Morris (2002). Profiles of Airborne Fungi in Buildings and Outdoor Environments in the United States. Appl Environ Microbiology; 68(4): 1743–1753
- Smith, E. Grant (2000). Sampling and Identifying Allergenic Pollens and Molds, Blewstone Press, San Antonio, Texas.
About the Author
Dr. Jackson Kung’u is a Microbiologist who has specialised in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analysed thousands of mould samples from across Canada. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at http://www.drjacksonkungu.com. Become a subscriber – FREE- for original reviews on mould and bacteria issues.