Identification of Aspergillus Species by Matrix-Assisted Laser Desorption Ionisation–Time-of-Flight Mass Spectrometry

Matrix-assisted laser desorption/ionisation–time-of-flight mass spectrometry (MALDI–TOF MS) has already been used routinely in clinical laboratories for rapid bacterial and yeast identification. However, its routine use for Aspergillus identification is still controversial because of a lack of unification of the culture method and a suboptimal database. In this study, we first examined the difference in using broth and agar plate cultures for growing the aspergilli before protein extraction and found that agar culture was much superior to broth culture in generating interpretable protein mass spectra. Then, based on the solid culture method, we examined the accuracy, with benA and/or CaM sequencing as the identification gold standard, in using MALDI–TOF MS for Aspergillus identification. Overall, the original Bruker Library could only identify 38.2% and 22.8% of the strains characterised at the genus/section and species level, respectively. When the Bruker Library was expanded with reference mass spectra generated from reference Aspergillus species in-house, the identification rates were improved to 61.0% and 48.0%, respectively. The MSI database, freely available online, outperformed the former two libraries for Aspergillus identification at all levels (genus: 95.1%, section: 92.7%, species: 74.8%). Agar plate culture and the MSI database should be used for MALDI–TOF MS identification of aspergilli in clinical laboratories.