Identification of dermatophytes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

In this study we evaluated the suitability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the identification of dermatophytes in diagnostic laboratories. First, a spectral database was built with 108 reference strains belonging to 18 species of the anamorphic genera Epidermophyton, Microsporum and Trichophyton. All strains were well characterized by morphological criteria and ITS sequencing (gold standard). The dendrogram resulting from MALDI-TOF mass spectra was almost identical with the phylogenetic tree based on ITS sequencing. Subsequently, MALDI-TOF MS SuperSpectra were created for the identification of Epidermophyton floccosum, Microsporium audouinii, M. canis, M. gypseum (teleomorph: Arthroderma gypseum), M. gypseum (teleomorph: A. incurvatum), M. persicolor, A. benhamiae (Tax. Entity 3 and Am-Eur. race), T. erinacei, T. interdigitale (anthropophilic and zoophilic populations), T. rubrum/T. violaceum, T. tonsurans and T. terrestre. Because T. rubrum and T. violaceum did not present enough mismatches, a SuperSpectrum covering both species was created, and differentiation between them was done by comparison of eight specific peptide masses. In the second part of this study, MALDI-TOF MS with the newly created SuperSpectra was tested using 141 clinical isolates representing nine species. Analyses were done with 3-day-old cultures. Results were compared to morphological identification and ITS sequencing; 135/141 (95.8%) strains were correctly identified by MALDI-TOF MS compared to 128/141 (90.8%) by morphology. Therefore, MALDI-TOF MS has proven to be a useful and rapid identification method for dermatophytes.

Matrix-Assisted Laser Desorption Ionization–Time of Flight (MALDI-TOF) Mass Spectrometry Using the Vitek MS System for Rapid and Accurate Identification of Dermatophytes on Solid Cultures

“…Several strains were also misidentified as T. violaceum (4/19 strains grown on SDA and 16/19 on SGC2). De Respinis et al (18) already showed a high degree of homology between T. violaceum and T. rubrum sensu lato by MALDI TOF MS. They could not achieve a direct identification and had to use the direct comparison of eight specific masses to reliably distinguish these two taxa.…”

“…Recent studies confirm that this technique may be very attractive for dermatophyte identification (18)(19)(20)(21)(22). In one study, the rate of correct identification of isolates belonging to the T. mentagrophytes complex was 89% (19), and in others, the overall rates of successful identification of dermatophyte species reached 95.8% (18), 97.8% (21), and 99.3% (20), demonstrating the potential of MALDI-TOF MS to replace classical identification methods. The technique has now also been used for the direct identification of dermatophytes in clinical samples (23).…”

“…A total of 134 reference strains belonging to 17 species of the genera Epidermophyton, Microsporum, and Trichophyton and characterized by genetic (internal transcribed spacer [ITS] sequencing) and morphological (18) analyses were used for the Vitek MS knowledge base creation (Table 1). They originated from culture collections (CBS, Utrecht, The Netherlands; Micoteca da Universidade do Minho, Braga, Portugal), external quality control programs, and individual collections (Department of Dermatology, University Hospital of Zurich, Zurich, Switzerland; Laboratory of Applied Microbiology, University of Applied Sciences and Arts of Southern Switzerland, Bellinzona, Switzerland).…”

“…In the second step, 131 clinical strains not used to build the knowledge base and belonging to 13 taxa were identified using the new knowledge base to validate its performance. Results were compared with sequencing and/or previous MALDI-TOF MS analyses carried out using the SARAMIS system (18).…”

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

“…Also, identification exclusively to the genus level was achieved for 18 (4.3%) and 11 (0.9%) isolates, respectively, in two studies (12,14). In the meantime, a homemade library for MALDI-TOF MS identification of dermatophytes was used in conjunction with the Bruker Biotyper library (version 3.0, which contained 3,995 unique reference spectra) to allow 93.0% and 59.6% of 171 clinical isolates to be identified to the genus and species levels, respectively (16); in another study, using the SARAMIS system, SuperSpectra were created for MALDI-TOF MS identification of dermatophytes, which resulted in 95.8% of 141 clinical isolates being correctly identified to the species level (17). To our knowledge, except for the NIH database, none of these in-house databases is publicly available so far, whereas the above-mentioned library by Sleiman et al is portable across diagnostic laboratories within Australia.…”