First Report of Cystobasidium slooffiae in Human Wounds from China: Molecular Identification and Clinical Insights

Cystobasidium spp. are rare yeasts recently recognized as emerging human pathogens. This study presents the first report from China of Cystobasidium slooffiae isolated from human wound infections, and characterizes its microbiological profile, phylogenetic identity, and antifungal susceptibility.

Two strains were isolated from skin wounds of immunocompromised patients. They were characterized based on colony morphology on Sabouraud dextrose agar, Gram staining, MALDI-TOF MS analysis, Erg11 amino acid sequences analysis, and phylogenetic analysis using combined sequences of 18S rDNA, D1/D2 domains, and ITS regions. Antifungal susceptibility testing was performed according to CLSI guidelines (M27-A3/M60).

The colonies transitioned from light yellow to orange within 48-96 h with Gram-positive budding cells. MALDI-TOF MS failed to identify accurately any of these strains. However, phylogenetic analysis of ITS confirmed that both strains were C. slooffiae. Both strains exhibited high minimum inhibitory concentrations (MICs) for all three echinocandins (>8 µg/mL) and fluconazole (32-64 µg/mL), whereas the MICs for isavuconazole were in the range 0.75-1 µg/mL. Erg11 sequence analysis revealed they formed a distinct clade that was genetically distant from Rhodotorulaceae.

Our findings showed that C. slooffiae could be an important emerging, opportunistic human invasive fungal pathogen because of its reduced susceptibility to echinocandins and fluconazole.