The mold Cladosporium was first described in 1816. Members of Cladosporium are widely distributed worldwide and commonly found on all kinds of plant material, soil, food, paint, textiles and other organic matters. They are also found colonizing as secondary invaders leaves infested by other plant pathogenic fungi.

Cladosporium spores represent the most common fungal component isolated from air. Being small, dry and usually formed in branched, easy to break chains, Cladosporium spores are well adapted to be easily released into the air and spread in large numbers over long distances.

Medical Relevance of Cladosporium Spores

Most members of Cladosporium group do not cause disease in humans. Cladosporium spores are of medical relevance given that long-term exposure to these spores can cause adverse health effects, including allergies and asthma symptoms.

The mechanism of sensitization of human beings by molds in general is not well understood. However, there are several possibilities, among them inhalation of dried mycelia in house dust or inhalation of spores from outdoor or indoor sources. It is well known that spores of Cladosporium are common in indoor and outdoor air. Cladosporium herbarum, for example, is an important cause of allergies.

While there no established safe or unsafe levels of airborne mold spores, a concentration of 3000 Cladosporium spores m³ in the air has been suggested as a threshold value for clinical significance.

Prevalence of Cladosporium Spores in Indoor Environment

Cladosporium is one of the most commonly recovered molds from indoor air followed by others such as Penicillium and Aspergillus. In summer the levels of Cladosporium spores in outdoor air are very high. In fact, most of the Cladosporium spores found in indoor environment in summer originate from outdoors.

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. Concentrations of Cladosporium species in indoor air is influenced by outdoor concentrations and indoor growth sources.

Common species of Cladosporium in Indoor Environment

In indoor environment, Cladosporium spp. occur as secondary wall colonizers after the primary ones such as Penicillium species, Aspergillus versicolor and Wallemia sebi. Cladosporium is 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 include:

• 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 by far the most prominent mould 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 moulds. 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 h 2 (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.

Conclusion

Regular detection, quantification and characterization of moulds in living and working environments are essential for exposure risk assessment to safe guard public health. Thus, monitoring Cladosporium spore concentration in indoor environments is important for indoor air quality control.

References

• Peternel R, Culig J, Hrga I: Atmospheric concentrations of Cladosporium spp. and Alternaria spp. spores in Zagreb (Croatia) and effects of some meteorological factors. Ann Agric Environ Med 2004, 11, 303-307.

• Flanning Brian, Samson, Robert A., and Miller, David J (Ed.). Microorganisms in home and indoor work environments: Diversity, Health Impacts, Investigation and control. Taylor and Francis, 2001.

• Samson, R. A., Hoekstra, E. S. and Frisvad, J. C. (Edit.). Introduction to Food- and airborne Fungi, 6th edition. Centraalbureau voor Schimmelcultures, 2000.
• Piecková E, Jesenská Z: Microscopic fungi in dwellings and their health implications in humans. Ann Agric Environ Med 1999, 6, 1–11.

• Bagni B, Davies RR, Mallea M, Nolard N, Spieksma FT, Stix E: Sporenkonzentrationen in Städten der Europäischen Gemeinschaft (EG). II Cladosporium und Alternaria Sporen. Acta Allergol 1977, 32, (English Abstract).

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 Cladosporium species:

• 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 from these types of mold 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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