Rapid one-step extraction method for the identification of molds using MALDI-TOF MS

Abstract

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has revolutionized fungal identification. Previously, we developed a MALDI-TOF MS mold extraction procedure and comprehensive database. While MALDI-TOF MS has become routine in a few laboratories, it has not yet become widespread. A major obstacle is the lack of a simple, reproducible and uniform protein extraction procedure. In this study, we developed and validated a rapid one-step protein extraction protocol for filamentous fungi. Excised molds were placed into tubes containing zirconia-silica beads and extraction solution without washing or ethanol inactivation steps. Extraction solutions containing different ratios of acetonitrile and formic acid were evaluated. Samples were then processed using a PowerLyzer high power bead based homogenizer and supernatants spotted for MALDI-TOF MS. The rapid method was evaluated prospectively and in parallel to our current mold extraction protocol for 3 months. Analysis of 106 clinical mold isolates resulted in an improved performance and a decrease in extraction time by 30 minutes to a total of 5 minutes of hands-on time. Acceptable identification scores (≥ 2.00) were achieved for up to 63.0% of mold isolates by the rapid method compared with 52.8% of isolates by the current routine protocol. Score comparisons between duplicate spots showed higher reproducibility of the rapid method as compared to the routine method. The rapid extraction method allows efficient analysis of clinical mold isolates both in scheduled batch runs and on an in-demand basis while providing a simple starting platform for laboratories adopting MALDI-TOF MS for mold identification.