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

PubMedID: 25851261In 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. © The Author 2015. Published by Oxford University Press on behalf of The International Society for Human and Animal Mycology

Dishwashers provide a selective extreme environment for human-opportunistic yeast-like fungi

Urban life has led to the creation of human-made environments that, from a microbiological perspective, provide extreme life conditions. Certain non-ubiquitous microorganisms such as thermophilic members of the black yeast genus Exophiala are enriched within these habitats for which no counterpart is known in nature. Dishwashers consistently accumulate a number of specific black, white and red yeasts on the rubber seals of doors and in stagnant water at the interior. Several of these yeasts are primarily known as agents of human opportunistic infections. In this review, the literature data are supported by a screening study involving 937 households in 15 cities in Turkey. Fungi were detected in 230 samples (24.5 %). Using rDNA sequencing, the prevalent species were identified as Exophiala dermatitidis (n = 116), Candida parapsilosis (n = 44), E. phaeomuriformis (n = 35), Magnusiomyces capitatus (n = 22), Rhodotorula mucilaginosa (n = 15), and C. lusitaniae (n = 14). The possible role of dishwashers in transmitting disease is discussed. © 2015, School of Science

ATR-FTIR Spectroscopy Highlights the Problem of Distinguishing Between Exophiala dermatitidis and E. phaeomuriformis Using MALDI-TOF MS

PubMedID: 26373644The present study compared two chemical-based methods, namely, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, to understand the misidentification of Exophiala dermatitidis and Exophiala phaeomuriformis. The study utilized 44 E. dermatitidis and 26 E. phaeomuriformis strains, which were partially treated with strong acids and bases for further evaluation. MALDI-TOF MS and ATR-FTIR spectroscopy data of the two Exophiala species were compared. Data groupings were observed for the chromic acid- and nitric acid-treated species when the black yeast sources were categorized as creosoted-oak sleepers, concrete sleepers, or dishwasher isolates. The MALDI-TOF MS data for the metalloenzyme-containing regions were consistent with the ATR-FTIR spectroscopy data. These results indicated that environmental isolates might contain metals not found in human isolates and might interfere with chemical-based identification methods. Therefore, MALDI-TOF MS reference libraries should be created for clinical strains and should exclude petroleum-associated environmental isolates. © 2015, Springer Science+Business Media New York