Discrimination of Aspergillus flavus from Aspergillus oryzae by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry.

Background: Aspergillus flavus is a major cause of severe non-invasive fungal infections in the Middle Eastern countries. However, it is difficult to distinguish A flavus from A oryzae.

Objectives: To assess the potential of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) in discriminating between A flavus and A oryzae and compare it with β-tubulin gene sequencing.

Methods: We used the Bruker Daltonik MALDI-TOF MS system to analyse 200 clinical and environmental A flavus isolates and one A pseudonomius and one A alliaceus (Aspergillus section Flavi) isolate a priori identified as such by sequencing of the β-tubulin gene.

Results: All 200 A flavus isolates were identified at the genus level and 176 (88%) at the species levels by MALDI-TOF MS based on the spectral log-scores (≥2.0 and 1.7-1.99, respectively); among them, only 18 (10.2%) were confirmed as A flavus, whereas 35 (19.9%) were identified as A oryzae and 123 (69.9%) as A flavus/A oryzae. Aspergillus pseudonomius and A alliaceus were misidentified as A flavus and A parasiticus with log-score values of 1.39 and 1.09, respectively.

Conclusions: The results indicate that the commercially available Bruker Daltonik MALDI-TOF MS score database cannot separate A flavus and A oryzae species. We also showed that establishment of an in-house library is a useful tool to discriminate closely related Aspergillus species, including A flavus and A oryzae.