Identification of Fungi by Conventional Microscopy Combined with Novel MALDI-TOF MS Mass Spectrometry

Abstract

　Fungi are usually identified by evaluating morphological characteristics. As fungi are rarely encountered in routine microbiology, it is important to have a suitable guide for the accurate identification of medically important fungi. This study was designed to improve identification of medically important fungi. A total of 20 clinical and reference fungal isolates, were used in this study. The examinations were conducted during the training period in the departments of clinical laboratory and dermatology at Juntendo University Hospital. For the identification of filamentous fungi, conventional culture, colony characteristics, and microscopic findings were collected via photographs. The macroscopic and microscopic morphologies of filamentous fungi showed similar characteristics to those of references. The chromogenic differential media, CHROMagar, was used for the identification of Candida spp. and Malassezia spp. Matrix-assisted laser desorption ionization-time of flight mass spectroscopy was used to rapidly and accurately identify Candida at the species level. Fourteen filamentous fungi and six yeasts were identified in this study using general resources such as Sabouraud dextrose agar (SDA), potato dextrose agar (PDA), and lactophenol cotton blue. The 14 fungi exhibited colony characteristics and microscopic findings on SDA and PDA at 30℃ for 2-14 d. In conclusion, using appropriate guides as tools for identification and implementing new testing technologies will enable the accurate identification of fungi. CHROMagar is extremely useful in rapid identification of common yeast species, improving and streamlining the work flow in clinical microbiology laboratories in the Kingdom of Thailand.