Fonsecaea Mold SpeciesFonsecaea species is a causative agent of Chromoblastomycosis and Mycetoma.
(Information from
www.doctorfungus.org
@ 2005) |
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Taxonomic Classifications
Kingdom:
Fungi
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Ecology Fonsecaea is a pigmented filamentous fungus isolated from soil, rotten wood, and decomposing plant material. Aside from being a saprophyte, it causes infections in humans as well. Cold – blooded animals living in swamps may also be infected. Most cases of infection come from tropical and subtropical regions. Fonsecaea exhibits in vivo dimorphism as it forms sclerotic fission cells only in tissue but grows as a mold in laboratory conditions.
Species The genus Fonsecaea only contains two species namely, Fonsecaea compacta and Fonsecaea pedrosoi.
Pathogenicity and Health Effects Fonsecaea is one of the causative agents of chromoblastomycosis which is described as a post – traumatic, chronic infection of subcutaneous tissues. The infection is characterized by verrucous cauliflower – like lesions and the formation of brown, sclerotic fission cells which appear like copper pennies in the tissue.
Most cases of infection come from tropical and subtropical regions. Fonsecaea pedrosoi is one of the major causative agents of chromoblastomycosis, particularly in South America and Japan. On the other hand, Fonsecaea compacta is a rare cause of chromoblastomycosis in tropical Central and North America. Systemic invasion succeeding chromoblastomycosis is very seldom.
Fonsecaea species may cause other human infections as well aside from chromoblastomycosis which include paranasal sinusitis, keratitis, and fatal brain abscesses following hematogenous dissemination have been reported.
Macroscopic Appearance Ø Growth rate is slow and colonies are restricted, flat to raised and folded with velvety to cottony texture on potato dextrose agar at 25°C; Ø Both surface and reverse is brownish black, olive, gray black or jet black in color; and Ø The filamentous appearance is maintained upon cultivation at a temperature of 25, 30, or 37°C.
Microscopic Appearance Ø Hyphae are septate, dark brown and conidiophores are cylindrical, pale brown, septate, sub – erect, slightly inflated at the tip, and sympodial with conidiogenous zones confined at the upper portion; Ø Blastoconidia are unicellular, ellipsoidal to round in shape and are formed in ranks successively; and Ø Conidia are brown and barrel – shaped with size ranging from 1.5 - 3 x 2.5 – 6 µm. There are four types of conidiogenesis that are observed among Fonsecaea species:
Fonsecaea type: One – celled conidia arise upon swollen denticles that are located at the conidiophore tips. These primary conidia become irregularly swollen at their apices and function as sympodial conidiogenous cells as well. Then, these conidia give rise to secondary conidia that are one – celled, pale brown on swollen denticles. Tertiary series of conidia are often produced by the secondary conidia which are similar to those formed by the primary conidia, resulting in a complex conidial head. This type of conidiogenesis does not form long chains of conidia and is primarily observed among the strains under the genus Fonsecaea.
Phialophora type: Vase – shaped conidia with collarettes are located at the tip of the phialides. This type of conidiogenesis is primarily observed for the strains of the genus Phialophora and may rarely be observed in strains of Fonsecaea as well.
Rhinocladiella type: One – celled, pale brown conidia are formed by the conidiophores which are sympodial and with denticles. These conidia may be located at the tips and along the sides of conidiophores. Secondary conidia are formed rarely. This type of conidiogenesis is primarily observed for the strains of the genus Rhinocladiella, but Fonsecaea strains may also exhibit such.
Laboratory Precautions Analyses involving Fonsecaea species must be carefully conducted in a biological safety cabinet.
Susceptibility Currently used to treat chromoblastomycosis are cryosurgery and itraconazole. The former is preferred for small lesions while the latter is applied to larger lesions. The combination of the two therapeutic modalities may also be used. In addition, terbinafine also shows promising response in treatment of chromoblastomycosis. In spite of this, chromoblastomycosis infection is difficult to treat and most therapeutic approaches provide only a modest success rate. |