Common indoor fungi

Alternaria

Alternaria is a genus comprising approximately 50 species of which most are saprophytes or plant pathogens. Alternaria alternata is an extremely common saprophyte found on plants, wood, wood pulp, textiles and food. It is cosmopolitan in distribution [grows worldwide]. A. alternata grows on the surfaces of leaves [phylloplane] and occurs in outdoor air at modest levels peaking in July or August depending on the location (reaching perhaps 500 spores/m3). The allergens of A. alternata can induce reactions at very low concentrations in sensitized individuals. Phylloplane strains of A. alternata i.e. those found in air, do not produce AAL toxin. Some produce the phytotoxin [compound toxic to plants] alternariol and related metabolites.

Aspergillus

Aspergillus is the asexual stage of a number of ascomycetes.Species of Aspergillus are distributed worldwide although they are somewhat more common in warmer climates. These species grow on a vast array of organic materials. Many species are cosmopolitan. There are 182 accepted species although only 40 occur with any frequency. Species of Aspergillus include several of considerable economic importance: A. flavus is the main producer of the potent carcinogen aflatoxin and A. fumigatus is an important cause of the invasive disease aspergillosis. Several species are common on building materials including A. versicolor. A. fumigatus is common in outdoor air in some regions in the fall, occurring on composting leaves and other materials.

Cladosporium

Cladosporium is a genus comprising approximately 500 species most of which are saprophytes or plant pathogens of which perhaps 20 are common. Cladosporium sphaerosphermum, C. cladosporoioides and C. herbarum are the most common species. All are found on plants, wood, wood pulp, textiles and food. Of the three, C. sphaerospermum is the species typically found on building materials. The other two are phylloplane species that occur in outdoor air at high levels, peaking in June, July or August depending on the location (reaching perhaps 10,000 spores/m3). Cladosporium herbarum produces a wide variety of allergens and approximately 10% of the population is sensitized to Cladosporium. Phylloplane strains of Cladosporium do not produce metabolites with material toxicity.

Penicillium

Penicillium is the asexual stage of a number of ascomycetes and species of Penicillium are distributed worldwide although they are somewhat more common in temperate climates. These species grow on a vast array of organic materials. Many species are cosmopolitan. There are 225 accepted species although only 70 occur with any frequency. Species of Penicillium include several of considerable economic importance: P. verrucosum produces ochratoxin on cereals and P. chrysogenum produces penicillin. Many Penicillium species cause damage in damp building materials including the toxigenic species P. aurantiogriseum.