Cladosporium is a leaf mould and one of the most common in outdoor and indoor air worldwide. It is a very common household mould in bathrooms, around tubs, shower stalls, or window frames and even bathroom walls and ceilings. Like every other mould, it requires free water for growth. Around the edge of the tub there is water from splashing or water running down the wall from the shower. The water just sits around the edge of the tub and may evaporate very slowly. On walls and ceilings the steamy air results in condensate, especially on colder, outer walls. The spores are ubiquitous and will germinate in this available water and very quickly little dark brown colonies start to grow. Eventually there will be an olive-brown to blackish brown growth of Cladosporium around the tub.
Some species of Cladosporium cause serious diseases to plants. The mold is commonly isolated from air, soil, foodstuffs, stored fruits, cereal grains, groundnuts, paint, and textiles. Cladosporium is a well known allergenic mould. The most common Cladosporium species in outdoor air are Cladosporium cladosporioides and Cladosporium herbarum. During summer there can be very high concentrations of airborne spores of Cladosporium cladosporioides and Cladosporium herbarum, and both contain allergenic proteins in their spores. Cladosporium cladosporioides and Cladosporium hebarum may be found colonizing painted metal surfaces of covering panels and vents of heating, air conditioning and ventilation systems.
Cladosporium sphaerospermum is the most predominant species growing in buildings. Studies have shown it can outgrow Penicillium chrysogenum because of its ability to re-initiate growth from the hyphal tips much faster than Penicillium species. Cladosporium sphaerospermum and occasionally Cladosporium herbarum is frequently isolated from indoor surfaces such as in bathrooms, windowsills and damp painted surfaces. It is also commonly found colonizing wood.
Species of Cladosporium are not known to produce any serious mycotoxins.
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Alternaria alternata is a well recognized allergen with airborne spores and mycelial fragments being responsible for the allergic symptoms in individuals with rhinitis or bronchial asthma. Alternaria sensitivity can also lead to severe and potentially fatal asthma. Studies have shown that up to 70 % of mould-allergic patients have skin test reactivity to Alternaria. It has also been shown that prolonged heavy exposure to Alternaria alternata spores and mycelial fragments mimics that of other allergens such as cat dander and dust mites. Since Alternaria is a seasonal mould then this type of allergy is more prevalent in the fall. A. alternata has also been recorded as an opportunistic pathogen causing skin diseases particularly in immunocompromised patients such as the bone marrow transplant patients.