showing sympodial development
of pale brown, fusiform to ellipsoidal, pseudoseptate,
poroconidia on a geniculate or zig-zag rachis.
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).
and Natural Habitats
is a dematiaceous, filamentous fungus. It is cosmopolitan in nature and is
isolated from plant debris and soil. The pathogenic species have known
teleomorphic states in the genus Cochliobolus and produce
genus Bipolaris contains several species. Among these, three
well-known pathogenic species are Bipolaris spicifera, Bipolaris
australiensis, and Bipolaris hawaiiensis.
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. Clinical manifestations include mycotic
keratitis, subcutaneous phaeohyphomycosis, sinusitis, peritonitis in
patients on continuous ambulatory peritoneal dialysis (CAPD), and cerebral
and disseminated infections.
and Clinical Significance
is one of the causative agents of phaeohyphomycosis. The clinical
spectrum is diverse, including allergic and chronic invasive sinusitis,
keratitis, endophthalmitis, endocarditis, endarteritis, osteomyelitis,
meningoencephalitis, peritonitis, otitis media (in agricultural field
workers),and fungemia as well as cutaneous and pulmonary infections and
allergic bronchopulmonary disease. Bipolaris can infect both
immunocompetent and immunocompromised host.
As well as being
isolated as saprophytes on plants, Bipolaris may be pathogenic to
certain plant species, particularly to Graminiae and also to animals, such
as the dog. It may cause nasal mycotic granuloma in the cattle. Bipolaris
may also be isolated as a laboratory contaminant.
Bipolaris colonies grow rapidly, reaching a diameter of 3 to 9 cm
following incubation at 25°C for 7 days on potato dextrose agar. The
colony becomes mature within 5 days. The texture is velvety to woolly. The
surface of the colony is initially white to grayish brown and becomes
olive green to black with a raised grayish periphery as it matures. The
reverse is also darkly pigmented and olive to black in color.
The hyphae are septate and brown. Conidiophores (4.5-6 µm wide) are
brown, simple or branched, geniculate and sympodial, bending at the points
where each conidium arises from. This property leads to the zigzag
appearance of the conidiophore. The conidia, which are also called
poroconidia, are 3- to 6-celled, fusoid to cylindrical in shape, light to
dark brown in color and have sympodial geniculate growth pattern. The
poroconidium (30-35 µm x 11-13.5 µm) is distoseptate and has a scarcely
protuberant, darkly pigmented hilum. This basal scar indicates the point
of attachment to the conidiophore. From the terminal cell of the conidium,
germ tubes may develop and elongate in the direction of longitudinal axis
of the conidium.
Teleomorph production of Bipolaris is heterothallic. The
perithecium is black in color, and round to ellipsoidal in shape. The
ascospores are flagelliform or filiform, hyaline in nature and are found
in clavate-shaped or cylindrical asci. Each ascus contains eight
No special precautions other than general laboratory
precautions are required.
susceptibility testing procedures have not been standardized for
dematiaceous fungi yet. Very limited data are available on susceptibility
of Bipolaris. These data suggest that itraconazole MICs are
variable and voriconazole MICs are considerably low.
Amphotericin B and
ketoconazole are used in treatment of Bipolaris infections.
Surgical debridement may be indicated in some cases, such as sinusitis.