Teleomorph: Cochliobolus sp.
Colonies are moderately fast growing, effuse, grey to blackish brown, suede-like to floccose with a black reverse. Microscopic morphology shows sympodial development of pale brown pigmented, pseudoseptate conidia on a geniculate or zig-zag rachis. Conidia are produced through pores in the conidiophore wall (poroconidia) and are straight, fusiform to ellipsoidal, rounded at both ends, smooth to finely roughened and germinating only from the ends (bipolar).
The genus Bipolaris contains about 45 species which are mostly subtropical and tropical plant parasites; however several species, notably B. australiensis, B. hawaiiensis and B. spicifera are well documented human pathogens. RG-1 organisms.
Bipolaris australiensis showing sympodial development of pale brown, fusiform to ellipsoidal, pseudoseptate, poroconidia on a geniculate or zig-zag rachis.
MIC data is limited. Antifungal susceptibility testing of individual strains is recommended.
Clinical manifestations include mycotic keratitis, subcutaneous phaeohyphomycosis, sinusitis, peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD), and cerebral and disseminated infections. Phaeohyphomycosis caused by Bipolaris species has been reported in both normal and immunosuppressed patients.
Drechslera, Bipolaris, Curvularia and Exserohilum are all closely related and differentiation of the genera relies upon a combination of characters including conidial shape, the presence or absence of a protruding hilum, the contour of the basal portion of the conidium and its hilum, the point at which the germ tube originates from the basal cell and, to a lesser degree, the sequence and location of the first three conidial septa. The table below is modified from Domsch et al. (1980).
|Drechslera||Conidia cylindrical, germinating from any cell, hilum not protuberant.||Pyrenophora|
|Bipolaris||Conidia fusiform-ellipsoidal, central cells not much darker and broader than the distal ones, hilum not protuberant, germination bipolar.||Cochliobolus|
|Curvularia||Conidia with 2-3 broader and darker central cells, often curved, with or without a prominent hilum, germinationbipolar.||Cochliobolus|
|Exserohilum||Conidia fusiform-cylindrical to obclavate, with a protuberant hilum, germination bipolar.||Setoshaeria|
Domsch, K.H., W. Gams, and T.H. Anderson. 1980. Compendium of soil fungi. Volume 1. Academic Press, London, UK.
Kwon-Chung, K.J. and J.E. Bennett. 1992. Medical Mycology. Lea & Febiger, Philadelphia and London.
McGinnis, M.R., M.G. Rinaldi and R.E. Winn. 1986. Emerging agents of Phaeohyphomycosis: pathogenic species of Bipolaris and Exserohilum. J. Clin. Microbiol. 24:250-259.