Black fungi: clinical and pathogenic approaches

Data are presented on the clinically relevant black yeasts and their relati ves, i.e., members of the Ascomycete order Chaetothyriales. In order to und erstand the pathology of these fungi it is essential to know their natural ecological niche. From a relatively low degree of molecular variability of the black yeast Exophiala dermatitidis, potential agent of brain infections in patients from East Asia, it is concluded that this species is an emergi ng pathogen, currently going through a process of active speciation. It is found to be an oligotrophic fungus in hot, moist environments, such as stea mbaths. Cladophialophora-, Fonsecaea- and Ramichloridium-like strains, know n in humans as agents of chromoblastomycosis, are frequently found on rotte n plant material, but the fungal molecular diversity in the environment is much higher than that on the human patient, so that it is difficult to trac e the etiological agents of the disease with precision. This approach has b een successful with Cladophialophora carrionii, of which cells resembling m uriform cells, the tissue form of chromoblastomycosis, were found to occur in drying spines of cacti. Phagocytosis assays provide a method to distingu ish between pathogens and non-pathogens, as the killing rates of strict sap robes proved to be consistently higher than of those species frequently kno wn as agents of disease. The therapeutic possibilities for patients with ch romoblastomycosis are reviewed.