The medically important dematiaceous fungi and their identification

Abstract

Summary. Dematiaceous fungi include a large group of organisms that are darkly pigmented (dark brown, olivaceous, or black). In most cases the pigment is melanin, and specifically, dihydroxyna‐phthalene melanin. The diseases produced include chromoblastomycosis, eumycotic mycetoma, and phaeohyphomycosis. Phaeohyphomycosis is a new classification for a diverse group of previously known entities grouped together on the basis of finding dematiaceous hyphal and/or yeast‐like forms in tissue; tissue involvement may be superficial, cutaneous and corneal, subcutaneous, or systemic. Identification of these fungi is based mostly upon morphology. Important structures include annellides (Phaeoannellomyces, Exophiala), phialides (Phialophora, Wangiella), adelophialides (Phialemonium without collarettes, Lecythophora with collarettes), differentiation of conidiophores (Xylohypha versus Cladosporium) and conidial hilum, septation and germination (Bipolaris, Drechslera, Exserohilum). Useful laboratory tests include the 12% gelatin test (controversial), nitrate assimilation (W. dermatiti‐dis is negative, most other species are positive), and determination of temperature maxima (especially 37 °C for E. jeanselmei, 40 °C for W. dermatitidis and B. spicifera, 42 °C for X. bantiana, and 45 °C for Dactylaria constricta var. gallopava and Sce‐dosporium inflatum). Zusammenfassung. Die Schwärzepilze (Dema‐tiaceae) stellen eine umfangreiche Gruppe von Organismen dar, die dunkel pigmentiert sind (dunkelbraun, olivfarben oder schwarz). In den meisten Fällen handelt es sich beim Pigment um Melanin, insbesondere um Dihydroxynaphthalenmelanin. Die Krankheiten, die diese Pilze verursachen, umfassen Chromoblastomykose, Eumyzetom und Phaeohyphomykose. Phaeohyphomykose ist eine neue Klassifikation für eine unterschiedliche Gruppe bereits früher bekannter Entitäten, bei denen Schwärzefadenpilze und/oder ‐hefepilze im Gewebe nachweisbar sind; der Gewebsbefall kann oberflächlich kutan und korneal, subkutan oder systemisch sein. Die Identifizierung dieser Pilze stützt sich vornehmlich auf ihre Morphologie. Wichtige Strukturen umfassen Anneliden (Phaeoannelomyces, Exophiala), Phialiden (Phialophora, Wangiella), Ade‐lophialiden (Phialemonium mit Kollaretten, Lecythophora mit Kollaretten), bedeutsam ist ferner die Differenzierung von Konidiophoren (Xylohypha versus Cladosporium) und konidialen Hila, die Sep‐tierung und Auskeimung (Bipolaris, Drechslera, Exserohilum). Wichtige Labortests sind der 12%‐Ge‐latine‐Test (umstritten), die Nitratassimilation (W. dermatitidis ist negativ, die meisten anderen Arten sind positiv) und die Bestimmung der Temperatur‐maxima (insbesondere 37 °C für E. jeanselmei, 40 °C für W. dermatitidis und B. spicifera, 42 °C für X. bantiana and 45 °C für Dactylaria constricta var. gallopava und Scedesporium inflatum).

Detection of Antibodies against Paracoccidioides brasiliensis Melanin inIn VitroandIn VivoStudies during Infection

“…For example, melanization protects P. brasiliensis yeast against amphotericin B, ketoconazole, fluconazole, itraconazole, and sulfamethoxazole (9,51). Additional beneficial effects of melanin in fungi include resistance to enzymatic degradation (3,5,10,15,20), UV light, heat, and desiccation (34, 44, 45). …”

Novel Exophiala Infection Involving Ulcerative Skin Lesions in Japanese Flounder Paralichthys olivaceus

“…Sections were stained with hematoxylin and eosin, and observed under light microscopy. The Schmorl's staining method was used to distinguish dark melanin pigments within the hyphal walls of dematiaceous fungi (Dixon and Polak-Wyss, 1991). Bacterial growth in the tissue was examined by Giemsa staining.…”

Update on Fungal Disease: From Establish Infection to Clinical Manifestation

“…One of the likely candidate virulence factors is the presence of pigment in the cell wall, which is common to all dematiaceous fungi [56]. Generally, this pigment is melanin, more specifically dihydroxynaphthalene melanin, a broadly stable compound that is important to pathogenicity, since it is resistant towards destructive physicochemical processes [57][58][59]. Several mechanisms have been proposed by which melanin may act as a virulence factor including: 1) a protective advantage against free radicals and hypochlorite which are produced by phagocytic cells in their oxidative defenses; 2) melanin may bind to hydrolytic enzymes preventing their action on the fungal plasma membrane; 3) the production of allergic reactions that can also cause disease [60].…”

“…Phaeohyphomycosis: Phaeohyphomycosis is a term used to cover the remainder of clinical syndromes caused by dematiaceous fungi [57,59]. These are opportunistic diseases whose predisposing factors are organ transplantation, leukemia, lymphoma, peritoneal dialysis, AIDS/HIV, corticosteroid therapy, and intravenous drug abuse.…”

“…Dematiaceous fungi, so-called darkly pigmented fungi, black yeasts, melanized fungi, comprise a heterogeneous group of organisms that have darkly pigmented (brown to black) cell walls of their hyphae or conidia [56,57].…”