Cladosporium, a well known trigger for asthmatic attacks, is one of the most widespread molds. It includes about 40 species naturally found in soil, on decaying plant material and as plant pathogens. Several studies conducted in Europe and North America have shown that Cladosporium spores are present in the outdoor environment throughout the year. However, concentrations are very low in winter. In summer, daily peaks may range from 2,000 to 50,000 spores per cubic meter of air. The concentration of Cladosporium species in indoor air is influenced by outdoor concentrations and indoor growth sources.
Common species of Cladosporium in Indoor Environment
In an indoor environment, Cladosporium spp. occur as secondary wall colonizers, appearing after the primary ones such as Penicillium species, Aspergillus versicolor and Wallemia sebi. Cladosporiumis very common on wet building material (e.g., gypsum board, acrylic painted walls, wood, wallpaper, carpet and mattress dust, HVAC fans, and wet insulation in mechanical cooling units).
The four most common species are:
- Cladosporium herbarum. An exceedingly common organism, found on dead herbaceous and woody plants, textiles, rubber, paper, and foodstuffs of all kinds. Indoors, it is found in floor, carpet and mattress dust, damp acrylic painted walls, wallpaper, HVAC insulation, filters and fans. Cladosporium herbarum is frequently the most prominent mold in air-spora. It grows over a wide range of temperatures, and has frequently been reported causing spoilage of meat in cold storage.
- Cladosporium sphaerospermum. This frequently encountered species has been isolated from air, soil, gypsum board, acrylic painted walls, painted wood, wallpaper, carpet and mattress dust, HVAC fans, wet insulation in mechanical cooling units, foodstuffs, paint and textiles.
- Cladosporium cladosporioides. A cosmopolitan species which has been isolated from meat, soil, air, textiles and paint.
- Cladosporium macrocarpum. A cosmopolitan species which has been isolated from dead plants, soil, indoor air, apple juice concentrates and seeds.
The Significance of Cladosporium in Indoor Air Quality
Species of Cladosporium are not human pathogens except in some cases of immuno-compromised patients. However, Cladosporium species have the ability to trigger allergic reactions to sensitive individuals. Prolonged exposure to elevated spore concentrations can elicit chronic allergy and asthma. Concentrations of 3000 Cladosporium spores per cubic meter of air are generally taken as the threshold concentrations for clinical significance. However, individuals may react at lower concentrations depending on their sensitivity. Spores of Cladosporium are formed in simple or branched loose chains. They vary greatly in size (5-40 x 3-13 µm) and shape (ovoid, lemon-shaped, oblong, spherical). They are easily detected in spore traps, although small single celled spores may be easily mistaken for spores of other molds. Only the small sized spores (about 0.6% of total airborne spores of Cladosporium) can penetrate into the terminal bronchi and alveoli in humans.
What is the Mechanism of Sensitization?
Cladosporium herbarum is the most important allergenic species. The most important allergens that have been reported from this species are Cla h 1 (Ag-32) and Cla h2 (Ag-54). However, research has shown that strains of Cladosporium herbarum differ in the content of these allergens. Sensitization is believed to occur through inhalation of dried mycelia in house dust or inhalation of spores from outdoor or indoor sources that contain the allergens. None of the allergens identified so far are spore specific.
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