Cladosporium is a common fungus in indoor and outdoor environment and is one of the most well known cause of allergy in sensitized individuals. Generally, exposure to mold occurs through inhalation, skin contact and ingestion. While all molds are potentially allergenic (i.e., can trigger allergy reactions) the amount of spores required to cause respiratory allergy symptoms has not been established and varies between different mold species and individual’s level of sensitivity. For example, 100 spores/m3 of air of Alternaria can trigger allergy symptoms whereas 3,000 spores/m3 of Cladosporium are required to cause allergy symptoms.
Cladosporium halotolerans (Source: Studies In Mycology 89: 177–301 (2018))
Identification of Cladosporium Species
The Genus Cladosporium currently has 218 recognized species. Identification of Cladosporium as a Genus is relatively easy. However, it is difficult to identify species of Cladosporium purely on morphological and cultural characteristics. Most isolates from air and from indoor environment have been found to belong to one of three species, that is, C. sphaerospermum (with spores often nearly spherical), C. cladosporioides (with smooth spores) and C. herbarum (with warty spores). For a long time, these 3 have always been thought to be species complex and this has now been confirmed in a worldwide study. The study showed that C. sphaerospermum is comprised of 23 morphologically similar but distinct species while C. cladosporioides and C. herbarum are comprised of 66 and 37 distinct species respectively.
Cladosporium species prevalent in indoor environments
In indoor environment, the common members of Cladosporium are also frequently isolated from air, food stuffs, paint, moist window sills, textiles and other organic substrates.
Currently 46 Cladosporium species frequently found in indoor environment have been fully described and illustrated. Sixteen of these Cladosporium species are new (i.e., being described for the first time). Of these 46, Cladosporium halotolerans was the most frequently isolated species indoors followed by C. sphaerospermum, C. pseudocladosporioides and C. allicinum in that order.
Cladosporium cladosporioides was reported to be the most predominant fungus in houses in Ontario and Atlanta and the most abundant fungus in outdoor air. As the composition of indoor species reflects the composition of outdoor species it’s therefore expected to find C. cladosporioides as dominant indoors.
References
K. Bensch, J.Z. Groenewald, M. Meijer, J. Dijksterhuis, K. Bensch, J.Z. Groenewald1, M. Meijer1, J. Dijksterhuis, Ž. Jurjević, B. Andersen, J. Houbraken, P.W. Crous, and R.A. Samson. Cladosporium species in indoor environments. STUDIES IN MYCOLOGY 89: 177–301 (2018).
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