Nature
Cladosporium is a heterogenous genus of hyphomycetes, consisting of more than 772 names (1). Cladosporium species are phylloplane fungi that grow on dead plant material and plant surfaces and common plant endophytes, which are pathogenic to humans and have saprobic nutrition (1, 2). C. herbarum is one of the most commonly studied fungal species in allergy research after Aspergillus fumigatus and Alternaria alternata. The spores of this mold are mostly found in outdoor air, but are also present indoors. (3). Of note, other species have been demonstrated to form the major part of Cladosporium genus burden on indoor surfaces (2).
The conidiophores of Cladosporium have significant features; typically, they are olive colored, almost erect, branched, and floccose. They produce numerous branched dry conidia with smooth to rough surfaces. A distinct darkened coronate hilum, or conidial scar characterized by a thick rim surrounding a central convex dome is present. (4, 5). They are 250 µm in length and 3-6 μm in width, with terminal and intercalary swellings (7-9 μm diameter) (5). Since the conidia are small and usually formed in branched chains, they are well adapted to be spread easily in large numbers over long distances via wind (6, 7). Hyphae are creeping, septate on the surface or in the substrate. Blastopores are 1-2 celled, sometimes 3 celled, with variable shape and size. (5).
Habitat
Cladosporium spp. are frequent airborne molds, which can be isolated from almost every environment and geographic location (4). They are found both in indoor and outdoor environments, with C. herbarum mainly found outdoors, and other species comprising most of the indoor Cladosporium communities (2). Unlike Penicillium chrysogenum and Aspergillus versicolor, which are predominant in the indoor environment following water damage, Cladosporium spp. thrive in ambient environmental conditions (2).
Additionally, Cladosporium spp. are commonly found to thrive on withering or fallen dead leaves. Generally, they are isolated from air, soil, food, paints, textiles, and several other substrates. (5, 6, 8). The optimal growth temperature of Cladosporium spp. is 25°C. Growth was not found for most species at 4 to 10°C and at 37°C. (5, 6) Spore release usually happens during wet as well as dry weather, particularly dependent on fluctuations in humidity. Their outdoor counts are higher during hot weather and storms (9).
Taxonomy
There are about 500 species in the genus Cladosporium. The species most commonly associated with disorders in humans are C. cladosporioides, C. oxysporum, C. sphaerospermum in addition to C. herbarum (4, 9).Below is the taxonomical hierarchy of Cladosporium herbarum (9).
Taxonomic tree of Cladosporium herbarum (9) |
---|
Domain |
Eukaryota |
Kingdom |
Fungi |
Phylum |
Ascomycota |
Class |
Dothideomycetes |
Order |
Capnodiales |
Family |
Davidiellaceae
|
Genus |
Cladosporium |
Species |
C. herbarum |
Taxonomic tree of Cladosporium herbarum (9) |
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Tissue
Fungi of the genus Cladosporium secrete various secondary metabolites such as thermostable mycotoxins, which persist during the normal preparation of food (5).