Bipolaris Species

SEPTATE OPPORTUNISTS

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.

DEMATIACEOUS OPPORTUNISTS

Opportunists with dark-colored hyphae may cause phaeohyphomycosis (infection caused by dematiaceous fungi).

PATHOGENICITY

Systemic, or disseminated, mycoses are infections that affect internal organs or deep tissues of the body. Frequently, the initial site of infection is the lung, from which the organism disseminates hematogenously to other organs or the skin. Generalized symptoms include fever and fatigue. Chronic cough and chest pain might also accompany these infections. Bipolaris frequently causes keratomycosis and fungal sinusitis, or occasionally subcutaneous abscesses or phaeohyphomycosis. Meningitis, allergies, and peritonitis also have been reported. Long-term therapy with amphotericin some, but not all, cases.

LABORATORY EVALUATION

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.

CULTURE

On SABHI agar at room temperature, the rapid-growing colony is velvety or woolly, at first appearing grayish-brown; later the center is matted and black, and the reverse is light or dark.

MICROSCOPIC

The septate hyphae are DARK. Numerous dark CYLINDRICAL, four- or five-celled POROCONIDIA with TRUNCATE HILA (points of attachment) are usually present in clusters along a BENT-KNEE shaped CONIDIOPHORE. When a poroconidium germinates, germ tubes may arise from one or both POLES (ends) and grow along the axis of the conidium. Bipolaris may be confused with the rarely pathogenic Drechslera ssp., but the poroconidia of the latter have rounded, nonprotruding hila and germ tubes that arise perpendicular to the axis of the conidium.