Evaluation of the Bruker Matrix-Assisted Laser Desorption–Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) System for the Identification of Clinically Important Dermatophyte Species

Abstract

Dermatophytes can invade the stratum corneum of the skin and other keratinized tissues and are responsible for a broad diversity of diseases of skin, nails and hair. Although the standard identification of dermatophytoses depends on macroscopic and microscopic characterization of the colonies grown on special media, there are a number of limitations owing to intraspecies morphological variability, atypical morphology or interspecies morphological similarity which entails improvement in the identification methods. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a novel method which proved to be effective for rapid and reliable identification of dermatophytes grown in cultures when compared to conventional methods. We evaluated the performance of Bruker MALDI-TOF MS System (Bruker Daltonics, Germany) for identification of clinically relevant dermatophytes. In order to increase the identification capacity of the system, we created supplemental spectral database entries using ten reference dermatophyte strains (ten species in two genera). The utility of the generated database was then challenged using a total of 126 dermatophytes (115 clinical isolates and 11 additional reference strains). The results were evaluated by both manufacturer-recommended and lowered cutoff scores. MALDI-TOF MS provided correct identification in 122 (96.8 %) and 113 (89.7 %) of the isolates with the lowered scores and using the supplemented database, respectively, versus 65 (51.6 %) and 17 (13.5 %) correct identifications obtained by the unmodified database and recommended scores at the genus and species levels, respectively. Our results support the potential utility of MALDI-TOF MS as a routine tool for accurate and reliable identification of dermatophytes.

Fast identification of dermatophytes by MALDI‐TOF/MS using direct transfer of fungal cells on ground steel target plates

“…We found only 14 out of the 149 strains with a LS below our defined thresholds but above should prompt clinicians to further assess the animal source of the infection. 4 Contrasting with previous findings, 8,9,21,22 Table S1). Of interest, a similar discrepancy was also obtained with B-MSPL which suggests that it is strain dependent.…”

“…This is of clinical relevance because these latter cannot be differentiated using common methods but require ITS gene sequencing and identification of zoophilic T. mentagrophytes should prompt clinicians to further assess the animal source of the infection . Contrasting with previous findings, we could discriminate T. violaceum from T. rubrum and T. soudanense by MALDI‐TOF/MS if cultures were made on PDA. However, T. benhamiae was not easily identified because low LS were frequently obtained irrespective of the medium used for subculture.…”

A survey among dermatologists: diagnostics of superficial fungal infections – what is used and what is needed to initiate therapy and assess efficacy?

“…For many years, the gold standard for diagnosis of superficial fungal infections has been direct microscopy often performed by the clinician, and culture sometimes supplemented by histopathology. Since the first dermatophyte polymerase chain reaction (PCR) was developed in 1996 an array of new molecular based methods for fungal identification have been developed with different PCR techniques and lately, matrix assisted laser desorption/ionization – time of flight (MALDI‐TOF) mass spectrometry has also been used . Because special equipment is required to perform molecular diagnostics the analysis is performed at specialized mycological or microbiological laboratories.…”

Identification of Molds by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

“…Although these methods can provide accurate results, they are expensive, require specialized equipment or expertise, and are not commonly available in clinical laboratories. In the present review, findings from the 10 studies (23)(24)(25)(27)(28)(29)(30)(31)(32)(33) shown in Table 1 indicate that before MALDI-TOF MS testing, only one study identified isolates via conventional phenotypical analyses (33), whereas almost all the remaining studies also sequenced all their isolates, and in two studies, only molecular biology analyses of the isolates were undertaken (27,28). This supports the idea that the overall high level of accuracy of MALDI-TOF MS-based mold identification shown in these studies might not be overestimated.…”

“…A more recent evaluation of the performance of the Bruker Biotyper system showed that MALDI-TOF MS provided correct genus-level and species-level identifications for 96.8% (122/126) and 87.9% (113/126) of dermatophyte isolates, respectively, using a supplemented database (the MALDI Biotyper Support Library, i.e., created by adding spectra from 10 reference dermatophyte strains) and decreased score values (33). Expectedly, rates of correct genus-level and species-level identifications of 51.6% and 13.5% were found when MALDI-TOF MS analyses were done by using the original database (MALDI Biotyper Library [MBL] version 3.1.2.0) and manufacturer-recommended score values (33).…”