Magnusiomyces capitatus and Saprochaete clavata are members of the clade of arthroconidial yeasts that represent emerging opportunistic pulmonary pathogens in immunocompromised patients. M. capitatus and S. clavata are physiologically differentiated by their growth responses to cellobiose, salicin, and arbutin. Despite these differences, misidentifications between the two species are frequent due to conflicting datasets. For this purpose, we adopted multilocus sequencing, amplified fragment length polymorphism (AFLP), phenotypic, and antifungal profiles for species delimitation. The present study can help to provide a stable nomenclature for this important group of fungi. We analyzed 34 reference strains obtained from Centraalbureau voor Schimmelcultures (CBS; housed at Westerdijk Fungal Biodiversity Institute, Utrecht, the Netherlands) with the goal of finding new genetic markers for classification using multilocus sequencing of (ITS, LSU, Rbp2, Act, and Tef1?) and amplified fragment length polymorphism (AFLP) fingerprinting. In addition to molecular data, physiological tests for the utilization of cellobiose, salicin, and arbutin and antifungal susceptibility profiles were tested following the Clinical and Laboratory Standards Institute M27-A3 document to verify whether there are any systematic differences in this newly defined group. Interspecific similarity using rDNA markers [internal transcribed spacer (ITS) and large subunit] was in the range of 96–99%, whereas that of protein-coding loci (Rbp2, Act, and Tef1?) was lower at 89.4–95.2%. Ultimately, Rbp2 was selected as the best marker for species distinction. On the basis of cloned ITS data, some strains proved to be misidentified in comparison with phenotypic characters, protein sequences, and AFLP profiles, indicating that different copies of the ribosomal operon were present in a single species. Antifungal susceptibility testing revealed that voriconazole had the lowest MIC against M. capitatus, while amphotericin B had the lowest MIC against S. clavata. Both species exhibited in vitro resistance to fluconazole and micafungin. In conclusion, we have provided detailed molecular characteristics of two species of arthroconidial yeasts, thereby greatly expanding the current database beyond rDNA ITS 365 sequence classification and incorporating new identification markers using multilocus sequence typing of various genes such as Rbp2. Moreover, antifungal testing revealed that voriconazole and amphotericin B are the most effective against these potential pathogens. Finally, based on our results, we suggest modifying the nomenclature of S. clavata according to updated fungal nomenclature guidelines.

7 / Molecular diagnostics of arthroconidial yeasts– frequent pulmonary opportunists