Rapid identification of VRE with MALDI-TOF MS

Abstract

Methods for the diagnosis of Vancomycin resistant Enterococci (VRE) include laborious time consuming phenotypic or costly molecular methods requiring appropriate facilities and staff. Mass spectrometry by matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF) can identify organisms rapidly and has shown promise in the identification of antimicrobial resistance. We sought to establish whether MALDI-TOF MS could be used to identify VRE. Consecutive Enterococcus faecium isolates phenotypically suspected and subsequently confirmed to be vanB positive by PCR over 18 months were analysed using the Bruker mi-croflex. Control groups were similarly analysed and the ability of MALDI-TOF MS to identify VRE was calculated using statistical tools in the proprietary software program ClinProTools. The Support Vector Machine model generated the highest recognition capability and cross validation (99.24% and 88.45%, respectively). The peak statistics for the five most important peaks showed a statistically significantly difference when comparing the VREs with the controls. Internal validations produced an average sensitivity of 92.4% and specificity 85.2%. Once established the method was incorporated into routine laboratory use and validated prospectively with a specificity of 98.1% and sensitivity of 96.7%. MALDI-TOF MS provides a rapid and accurate method for the identification of VRE with significant implications for the clinical microbiology laboratory and hospital infection control.