Pathogenic Mold Pathogenic Molds Disease Causing Mold Pathogenicity Infecteous Molds

DISEASE CAUSING MOLD

Pathogenic molds usually produce some type of infection. The word pathogenic literally means, "capable of causing disease". A normal, healthy individual can probably resist infection by these organisms regardless of dose, however, pathogenic molds can cause serious health effects in persons with suppressed, underdeveloped, or compromised immune systems. In some cases, high exposure may cause hypersensitivity pneumonitis (an acute response to exposure to an organism). People with compromised immune systems would be, infants and small children whose immune systems are not fully developed, elderly people whose immune systems are essentially worn out, and anyone exposed to AIDS, chemotherapy, pneumonia, bronchitis, and other respiratory infections.

Bipolaris Species
The U.S. Government's Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Bipolaris mold: Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis.

Bipolaris australiensis 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).


Description and Natural Habitats
Bipolaris 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 ascospores.

 
Species
The genus Bipolaris contains several species. Among these, three well-known pathogenic species are Bipolaris spicifera, Bipolaris australiensis, and Bipolaris hawaiiensis. 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. Clinical manifestations include mycotic keratitis, subcutaneous phaeohyphomycosis, sinusitis, peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD), and cerebral and disseminated infections.

Pathogenicity and Clinical Significance
Bipolaris 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.

Macroscopic Features
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.

Microscopic Features
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 ascospores.

Laboratory Precautions
No special precautions other than general laboratory precautions are required.

Susceptibility
In vitro 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.

 

Pathogenic Mold Pathogenic Molds Disease Causing Mold Pathogenicity Infecteous Molds

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