Aspergillus fumigatus is a thermotolerant/thermophilic fungus capable of growing over a wide temperature range (12°C–53°C). It has a worldwide distribution. Being thermotolerant, it is a significant component of compost microflora.
Health effects associated with Aspergillus fumigatus
The spores of Aspergillus fumigatus are very small. Having a diameter of 2–3.5 µm, they are easily inhaled deep into the lungs. It is estimated that people inhale at least several hundreds of spores of Aspergillus fumigatus per day without harm. However, Aspergillus fumigatus is an opportunist pathogen (Hazard Risk Group 2) and can cause a lung infection (aspergillosis), in people with weak immune system. Most of the cases of aspergillosis are caused by this fungus. Because of its potential role as an opportunist pathogen, there is concern about high concentrations of Aspergillus fumigatus spores in the vicinity of hospitals, where those with compromised immune system such as organ transplant and cancer patients, may be at increased risk of infection. Therefore, monitoring for airborne spores in hospitals especially during renovations is a good practice.
Occurrence of Aspergillus fumigatus
Aspergillus fumigatus naturally occurs in decaying organic material, but because it is a thermotolerant fungus it grows well at raised temperatures experienced during the composting process. Within the indoor environment, A. fumigatus belongs to the group of indicator microorganisms typical of moisture-damaged buildings such Stachybotrys, Chaetomium, Fusarium and Ulocladium. The following characteristics make A. fumigatus a ubiquitous opportunistic pathogen: 1) ability to survive and grow in a wide range of environmental conditions, 2) effective dispersal in the air, 3) physical characteristics that allow spores to reach deep into the respiratory system, and 4) ability to swiftly adapt to the host environment.
Air Sampling for Aspergillus fumigatus
In hospital environment, air sampling may be conducted to monitor air quality during construction, to verify filter efficiency, or to commission new space prior to occupancy. Because aspergillosis cases have occurred when airborne fungal spore concentrations ranged as low as 0.9–2.2 colony-forming units per cubic meter (CFU/m3) of air, it is suggested that an air volume of at least 1000 L (1 m3) should be considered when sampling highly filtered areas.
Sampling media and incubation temperature for Aspergillus fumigatus
Malt extract agar (MEA) can be used to sample for Aspergillus fumigatus. For selective isolation of A. fumigatus, a high incubation temperature of 37 to 40 is then used as this inhibits growth of other saprophytic fungi.
References
- Kwon-Chung, K. J., & Sugui, J. A., 2013. Aspergillus fumigatus—What Makes the Species a Ubiquitous Human Fungal Pathogen? PLoS Pathogens, 9(12), e1003743. http://doi.org/10.1371/journal.ppat.1003743
- Sehulster, L. et al., 2003. Guidelines for environmental infection control in health-care facilities. Morbidity and Mortality Weekly Report Recommendations and Reports RR, 52(10).
- Swan, J. et al., 2003. Occupational and environmental exposure to bioaerosols from composts and potential health effects: a critical review of published data, HSE Books.
- Streifel, A. et al., 1983. Aspergillus fumigatus and other thermotolerant fungi generated by hospital building demolition. Applied and environmental microbiology, 46(2), pp.375–378.
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