6.2.1 Alternaria

A number of very similar, related species are usually grouped together as Alternaria. The spores of Alternaria are multicelled and developed in chains, head-to-toe, from which their name derives. Spores are multiseptate, both transverse and longitudinally. They vary in width and length according to species, usually 8-75 ц,т long; some species such as A. longissima are up to 0.5 mm long. Alternaria, which is both ubiquitous and abundant, is both saprophytic and parasitic on plant material and is found on rotting vegetation as well as in damp indoor areas, such as bathrooms. Some species of Alternaria are the imperfect, asex­ual, anamorph spores of the ascomycete Pleospora.

6.2.2 Aureobasidium

Aureobasidium is common in both outdoor and indoor air, bathroom walls, and shower curtains. Aureobasidium causes mildew and has been isolated in flooded areas of buildings, as well as from soils, plants, and other substrates. Aureobasidium has been associated with hypersensitivity pneumonitis in some individuals.

6.2.3 Cladosporium

Cladosporium, composed of over 500 species, is found in outdoor as well as indoor air. Cladosporium has been isolated from fuels, wood, plant tissues, straw, face cream, air, soil, foods, paint, and textiles. Cladosporium spores are often found in higher concentrations in the air than any other fungal spore type.

Cladosporium bears copious numbers of spores on branched conidiophores. The spores usually have distinctive "scars" at both ends where they are joined both to the spore at one end and to the conidiophore at the other. Although often identified as single-celled spores, spores are frequently seen with a single transverse septum or several transverse septa. Their length ranges from 4 to 20 |xm.

Cladosporium (Hormodendrum) is the most commonly identified outdoor fungus and is a common indoor air allergen. Indoors Cladosporium may be different from the species identified outdoors. Cladosporium is commonly found on the surface of fiberglass duct lin­ers in the interior of supply ducts. Cladosporium can cause mycosis and is a common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms; chronic cases may develop pulmonary emphysema.

6.2.4 Rhodotorula

Rhodotorula is a commonly isolated yeast that is frequently isolated from humidifiers and soil. Rhodotorula may be allergenic to susceptible individuals when present in sufficient concentrations.

6.2.5 Stemphylium

Stemphylium is a saprophytic fungus (grows on nonliving organic material) commonly found on cellulosic materials (that is, of plant origin, including livestock feed, cotton cloth, ceiling tiles, paper). Stemphylium is an example of a diurnal sporulator. An alternating light and dark cycle is required for spore development. This fungus requires ultraviolet light for the production of conidiophores; however, the second developmental phase, when the conidia are produced, requires a dark period. Stemphylium also requires wet conditions for growth. Stemphylium spores range from 23 to 75 (xm in length.

6.2.6 Sterile Fungi

Sterile fungi are common to both outdoor and indoor air. These fungi produce vegeta­tive growth, but yield no spores for identification. Their presence will increase CFU/1. Derived from ascospores or basidiospores, the spores of which are likely to be allergenic, these fungi should be considered allergenic.

6.2.7 Yeast

Various yeasts are commonly identified on air samples. Yeasts are not known to be allergenic, but they may cause problems if a person has had previous exposure and devel­oped hypersensitivities. Yeasts may be allergenic to susceptible individuals when present in sufficient concentrations. Yeast grows when moisture, food, and just the right tempera­tures are available.