Purpose: The Bruker MALDI-TOF MS system had launched the commercial filamentous fungi library which made identification of Apergillus by MALDI-TOF MS possible, and favorable performances were presented in some previous studies with the recommended protocol by the manufacturer including fungi liquid sub-inoculation which is not usually used in the clinical labs. In our study, we evaluated the practicability of the Bruker MALDI-TOF MS with its commercial Filamentous Fungi database in identifying clinical isolates of Aspergillus grown directly on solid agar media, a widely employed culture method in labs.
Methods: A total of 381 isolates of Aspergillus isolated from clinical specimens were collected and identified to species level by molecular sequencing of ITS and β-tubulin or calmodulin genes. All isolates were incubated on Sabouraud Dextrose Agar plates and the outer mycelia of the colonies were collected for MALDI-TOF analysis after 2 to 3 days incubation without further liquid sub-inoculation. The Formic acid Acetonitrile treatment for the mycelia materials and the remaining analysis steps were carried out with reference to the standard.
Results: Applying the standard interpretative criteria recommended by the manufacturer, i.e., a species cutoff value of ≥2.000 and a genus cutoff value of 1.700-1.999, the Bruker MALDI-TOF system identified 30.2%(115/381 ) of these isolates to the species level and 49.3%(188/381) to the genus level. From another aspect, correct species-level identification could be gained in 89.0% (339/381) isolates by the Bruker MALDI-TOF MS with reference to the molecular sequencing results regardless of the MS score values obtained and the criteria cutoff recommended. When the identification cutoff value was lowered from 2.000 to 1.700, the species-level identification rate increased to 79.5%(303/381) with a slight rise of false identification from 2.6%(3/115) to 4.9%(15/303).
Conclusion: The Bruker Biotyper MALDI-TOF MS system had a fairish performance in identifying Aspergillus directly grown on solid agar media. Adoption of alternative cutoff values for interpretation and continued expansion of the Bruker Biotyper MALDI-TOF MS database are required to improve the performance of the system for identifying highly diverse species of clinically encountered Aspergillus isolates.
Full conference title:
- AAA 8th (2018)