Identification of filamentous fungi including dermatophytes using MALDI-TOF mass spectrometry

Abstract

Identification of filamentous fungi based on morphological features is the most available approach used in clinical mycology laboratories. However, MALDI-TOF mass spectrometry is currently invaluable for identification of microorganisms because of its rapidity, simplicity, and accuracy. This study aimed to find the optimal way of identifying filamentous fungi using MALDI-TOF MS.The sample comprised 193 isolates of filamentous fungi. The identification started with morphological assessment. Then isolates were identified using MALDI-TOF MS, both directly from culture and following culture in liquid media with extraction. Subsequently, identification of 20 selected isolates was compared by sequencing of the benA gene, ITS1-5,8-ITS2, and D1-D2 LSU regions.Based on morphological criteria, 17 genera of fungi were identified. With MALDI-TOF MS performed directly from culture, nine isolates were identified to the genus level and 184 to the species level, with a total of 75 species being noted. With the MALDI-TOF MS extraction method, 190 isolates were identified to the species level, with 43 species being noted. The rates of agreement between identification using morphology and the MALDI-TOF MS direct method were 58.55% at the genus level and 22.24% at the species level. The rates of agreement between identification using morphology and the MALDI-TOF MS extraction method were 84.97% at the genus level and 46.11% at the species level. Using sequencing, 87.5% agreement was found for identification with the MALDI-TOF MS extraction method, as compared with only 43.75% for the direct method.The results suggest that the optimal approach to identification of filamentous fungi is a combination of morphological features and MALDI-TOF MS using the extraction method.