ABSTRACT
Yeasts are generally defined as unicellar fungi. Numerous yeasts are able to form hyphae and/or pseudohyphae, however. Yeasts are polyphyletic in origin and belong to the Ascomycetes and the Basidiomycetes (1). Within the Basidiomycetes, they occur in all three main phylogenetic lines, namely the Hymenomycetes [Cystofilobasidiales, Trichosporonales, Tremellales (jelly fungi), and Filobasidiales], the Urediniomycetes (Sporidiales, and including the obligate plant parasitic rust fungi), and the Ustilaginomycetes (Malasseziales, and including the plant parasitic smut fungi; Fig. 1) (2). Medically important basidiomycetous yeasts belong to the genera Cryptococcus Vuillemin, Trichosporon Behrend (both Hymenomycetes), and Malassezia Baillon (Ustilaginomycetes). Other basidiomycetous yeasts that have been reported from patients occur in the genera Rhodotorula FC Harrison and Sporobolomyces Kluyver & van Niel (both Urediniomycetes). Yeasts, including the basidiomycetous ones, are usually identified by using medical physiological characteristics. Summarized physiological data of the most important basidiomycetous yeasts are presented in Tables 1 and 2.
