Dermatophyte Identification Using Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

Abstract

The performance of the Bruker Biotyper matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometer (MS) for the identification of dermatophytes from clinical cultures was compared to that of dermatophyte identification using 28S rRNA gene sequencing. The MALDI Biotyper library (MBL; version 3.0) was used alone and in combination with a supplemented library containing an additional 20 dermatophyte spectra (S-MBL). Acquired spectra were interpreted using both the manufacturer-recommended scores (genus, >1.7; species, >2.0) and adjusted cutoff values established by this study (genus, >1.5; species, >1.7); identifications required a minimum 10% difference in scores between the top two different organisms to be considered correct. One hundred well-characterized, archived dermatophyte isolates and 71 fresh dermatophyte cultures were evaluated using both libraries and both sets of cutoff criteria. Collectively, the S-MBL significantly outperformed the MBL at both the genus (93% versus 37.4%; P < 0,0001) and species (59.6% versus 20.5%; P < 0.0001) levels when using the adjusted score criteria. Importantly, application of the lowered cutoff values significantly improved genus (P ‫؍‬ 0.005)-and species (P < 0.0001)-level identification for the S-MBL, without leading to an increase in misidentifications. MALDI-TOF MS is a cost-effective and rapid alternative to traditional or molecular methods for dermatophyte identification, provided that the reference library is supplemented to sufficiently encompass clinically relevant, intraspecies strain diversity.Dermatophytes, comprising species within the genera Epidermophyton, Microsporum, and Trichophyton, exclusively invade and infect keratinized tissues (i.e., hair, skin, and nails). These organisms are among the most common fungal infections in humans, accounting for over 5 million physician visits annually in the United States (7, 26). Dermatophytes primarily cause superficial dermal mycoses and rarely progress to more invasive disease (8). In the United States, Trichophyton rubrum remains the most common cause of tinea infections and the most frequently isolated dermatophytic pathogen (7,24).Laboratory identification of dermatophytes is typically based on macroscopic observation of colony morphology (i.e., pigmentation, growth rate, texture, etc.) on selective media, followed by microscopic examination of conidia. In addition, specialized Trichophyton agars may be used for differentiation of species within the genera (14). These phenotypic techniques require experienced technologists and are often labor-intensive with a prolonged turnaround time. With the advancement of modern molecular techniques, some laboratories have turned to dermatophyte identification schemes involving sequencing of specific ribosomal DNA regions or real-time PCR amplification of discrete genes (2, 20). While these methods are highly accurate and rapid, they are costly and can be complex to implement.Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) m...

Evaluation of the Vitek MS Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry System for Identification of Clinically Relevant Filamentous Fungi

“…Previous studies have shown that MALDI-TOF MS is a rapid and accurate method for the identification of dermatophytes. There have been many studies examining this group of molds, with identification rates of Ͼ90% for these studies (12,13,(20)(21)(22). Our study correctly identified 100% (14/14) of the dermatophytes tested.…”

“…Prior studies have evaluated the accuracy of MALDI-TOF MS for the identification of only a few genera or groups of organisms, such as Aspergillus spp. or the dermatophytes (12,13,(19)(20)(21)(22)(23)(24)(25)(26). In our study, which examined 319 isolates from 43 different genera, the Vitek MS version 3.0 library was able to correctly identify 66.8% of isolates and 76.8% of the isolates after additional SARAMIS analysis.…”

“…For filamentous fungi, databases have been limited, and unlike bacteria, filamentous fungi require additional processing steps to disrupt the cell wall, extract proteins, and inactivate the isolate (10). These additional processing steps and limited libraries have led laboratories to develop their own methodologies and databases to overcome these barriers to adoption (11)(12)(13). These limitations have hindered widespread implementation of this technology in the clinical laboratory for the identification of filamentous fungi.…”

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

“…D ermatophytes in the genera Epidermophyton, Microsporum, and Trichophyton are usually characterized and identified by cultural and morphological characters and physiological tests or, more recently, by sequencing (1). Morphological identification is time-consuming and complex, usually requiring expert mycological knowledge, while sequencing is comparatively expensive and at least 2 to 3 days elapse before sequencing results are available.Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) is a reliable technique for the identification and typing of microbial pathogens such as bacteria (2-7), yeasts (8-10), and filamentous fungi, including dermatophytes (7,(11)(12)(13)(14)(15)(16)(17). Recent studies confirm that this technique may be very attractive for dermatophyte identification (18-22).…”

“…Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) is a reliable technique for the identification and typing of microbial pathogens such as bacteria (2-7), yeasts (8-10), and filamentous fungi, including dermatophytes (7,(11)(12)(13)(14)(15)(16)(17). Recent studies confirm that this technique may be very attractive for dermatophyte identification (18-22).…”