Optimizing MALDI-TOF MS for routine dermatophyte identification, including Trichophyton indotineae.

BACKGROUND: Dermatophytosis is a common superficial fungal infection worldwide, and the recent global spread of the terbinafine-resistant fungus Trichophyton indotineae has made rapid, accurate species identification a priority for clinical laboratories. This study assessed the identification performance of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) using molecularly identified dermatophyte isolates recovered from chronic, recalcitrant, and widespread infections. METHODS: A total of 134 dermatophyte isolates were analyzed, including 119 Trichophyton indotineae, 10 T. rubrum, 3 T. tonsurans, and 2 Microsporum canis. Isolates were cultured on ID Fungi Plates (IDFPs), Sabouraud glucose agar (SGA), and Kimmig agar and incubated at 27 °C for 72 h. MALDI-TOF MS analysis was performed using the VITEK® MS PRIME system. Identification performance was compared across the three culture media. RESULTS: IDFP achieved the highest species-level identification rate (97.8%), followed by SGA (87.3%) and Kimmig agar (75.4%). For T. indotineae, species-level identification was also highest with IDFP (97.5%), followed by SGA (88.2%) and Kimmig agar (74.8%). CONCLUSIONS: These findings support the use of MALDI-TOF MS as a rapid and practical tool for routine dermatophyte identification and highlight the importance of optimized culture conditions for maximizing diagnostic performance. A simple, inexpensive change in laboratory workflow can therefore make routine identification of dermatophytes, including T. indotineae, reliable enough for everyday diagnostic use.