Performance comparison of mould identification by Bruker and VITEK matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Filamentous fungal, or mould, infections are a major cause of morbidity and mortality in immunocompromised patients, requiring rapid and accurate identification for appropriate clinical management. Conventional culture-based identification of moulds may require long culture times and careful gross and microscopic morphologic identification by highly experienced technologists. However, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has shown promise for faster identification of cultured moulds. We compared the agreement of Bruker MALDI Biotyper Filamentous Fungi Library 4.0 identification with VITEK MS Knowledgebase Library 3.2 identification of 149 mould culture isolates collected for routine patient care from two hospitals, comprising 35 species or species-complexes. Sequencing and/or culture morphology were used to identify moulds that were discordantly identified by the two platforms. Sequencing was performed on all Fusarium species isolates, which cannot be differentiated morphologically. All isolates were concordantly identified by the two MALDI-TOF MS systems at the genus level except for one isolate (99%). Species-level concordance between the two systems was achieved at 81% (120/149). Five (9.8%) isolates of Fusarium species were concordantly identified by the MALDI-TOF MS systems but identified as a different species or species-complex by gene sequencing. Three fungal species considered concordantly identified by MALDI-TOF MS systems exhibited nomenclatural inconsistencies. Although their databases and methods differ, current VITEK and Bruker MALDI-TOF MS systems have high concordance for identification of most common moulds isolated in clinical microbiologic laboratories, but users should be aware of performance limitations and nomenclature differences.