ABSTRACT
The term Pneumocystis carinii names not only one taxonomic entity but a heterogeneous group of unicellular eukaryotic parasitic organisms included in the genus Pneumocystis, which has definitely been assigned to the fungal kingdom. Host species-related differences among Pneumocystis organisms from different mammalian species have been revealed at the genomic [1-8] and phenotypic levels, including ultrastructural morphology [9-12] or selective infectivity [9,13-16]. Pneumocystis jiroveci Frenkel 1999, formerly P. carinii f. sp. hominis [17,18], was the sole species identified in humans until recently. As viable isolates of P. jiroveci developed only limited growth in culture [16] and did not infect laboratory animals [16,19], most studies on Pneumocystis cellular biology were developed by using parasites of animal origin.
