Alternaria spp. are found worldwide on grasses and leaves. They have been implicated in tomato rot and are readily recovered from the environment in air-settling plates.
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).
Alternaria spp. is generally medically implicated in chronic fungal sinusitis. Patients are often misdiagnosed and treated for an extended period for bacterial sinusitis. The infection rarely spreads beyond the sinuses in immunocompetent hosts but can be found systemically in those suffering from immune suppression. It has been reported in keratomycosis, skin infections, osteomyelitis, pulmonary disease, and nasal septum infection.
Microscopic evaluation reveals short conidiophores bearing conidia in chains that lengthen in an acropetal fashion. Multicelled conidia have angular cross walls and taper toward the distal end. Alternaria spp. are phaeoid, rapidly growing fungi with colonies ranging from shades of gray to brown to black.
On SABHI agar at room temperature, the light gray, woolly colony rapidly matures to dark greenish black or brown, with a black reverse.
Reproductive structures and hyphae are DARK. The CHAINED PORO-CONIDİA, which contain HORIZONTAL and VERTICAL SEPTA, have club-shaped bases with tapered apices. If the poro-conidia are not in chains, they may be mistaken for the opportunist Stemphylium.