MALDI-TOF MS-based identification of black yeasts of the genus Exophiala

In this study, we investigated the applicability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the identification of Exophiala species. The analysis included a total of 110 Exophiala isolates, including 15 CBS strains representing 4 species, Exophiala dermatitidis (61), E. phaeomuriformis (36), E. crusticola (9), and E. heteromorpha (4), that had been previously identified based on internal transcribed spacer (ITS) regions. We also compared the relative efficacies of Sabouraud glucose agar (SGA) and Columbia agar (CA) for use in MALDI-TOF MS. Remarkably, we obtained a log-score value ≥2.0 by using either SGA or CA for all 15 CBS strains, indicating species-level identification. The remaining 95 Exophiala strains were identified to the genus or species levels, with identification rates of 96.8% and 90.5%, using SGA or CA, respectively. Most of the E. dermatitidis (100% and 92.9%), E. phaeomuriformis (80.6% and 83.9%), E. crusticola (50% and 100%), and E. heteromorpha (100% and 100%) isolates were correctly identified using SGA or CA, respectively. Furthermore, 58.9% and 26.3% of the strains had log-score values of ≥2.0 by using SGA and CA, respectively. Our results indicate that MALDI-TOF MS is a rapid and reliable technique with high rates of correct taxonomic identification.