These fungi are found in the environment and have a predilection for cellulose products. They have been known to devastate printed literature and library holdings and have been associated with indoor air quality problems.
Hyphae of most opportunists molds contain cross-walls. Those of medical importance fall into the phylum Deuteromycota. The septate opportunistic molds may be divided into those that are dematiaceous (dark-colored hyphae and/or conidia), and those that are hyaline (light colored hyphae and conidia). Organisms with dark hyphae on tease mounts also have dark green to black colonies, especially on the colony reverse. The colonial color aids in the initial identification. Hyaline organisms exhibit light-colored colonial aerial hyphae, but they may be covered over with brightly colored comidia; thus, a tease mount is required. In the following descriptions, key identifying features are capitalized.
Opportunists with dark-colored hyphae may cause phaeohyphomycosis (infection caused by dematiaceous fungi).
Infections by Chaetomium organisms have been reported in the brains of patients with central nervous system disease. Several of these patients have been identified as intravenous drug abusers.
Colonies are moderately rapid to rapidly growing and begin dirty gray, becoming phaeoid with age. Some species produce a diffusible pigment that turns the agar completely red.
Microscopically, numerous perithecia are typically seen. These perithecia are pineapple-shaped and are ornamented with straight or curled hairs or setae. The asci contained within the perithecia are evanescent, so at maturity the pigmented, lemon-shaped ascospores are released within the perithecium.