Typing of vancomycin-resistant enterococci with MALDI-TOF mass spectrometry in a nosocomial outbreak setting

• DOI: 10.1016/j.cmi.2018.03.020
• Publication Date: 2018-03-23T22:57:43Z
• Authors: B.J. Holzknecht; R. Dargis; M. Pedersen; M. Pinholt; J.J. Christensen; Anette M. Hammerum; Pia Littauer; Peder Worning; Henrik Westh; Claus Moser; Ulrik S. Justesen; Lars E. Lemming; Turid S. Søndergaard; Esad Dzajic; Tove Ejlertsen
• Keywords: 0301 basic medicine; Enterococcus faecium; Vancomycin-Resistant Enterococci/classification; Disease Outbreaks; Vancomycin-Resistant Enterococci; 03 medical and health sciences; Bacterial Typing Techniques/methods; Matrix-Assisted Laser Desorption-Ionization/methods; MALDI-TOF MS; Humans; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods; Gram-Positive Bacterial Infections/microbiology; Gram-Positive Bacterial Infections; Enterococcus faecium/classification; Cross Infection; Spectrometry; Reproducibility of Results; Mass; Bacterial Typing Techniques; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; VREfm; Cross Infection/microbiology; Vancomycin resistance

To investigate the usefulness of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) typing as a first-line epidemiological tool in a nosocomial outbreak of vancomycin-resistant Enterococcus faecium (VREfm).Fifty-five VREfm isolates, previously characterized by whole-genome sequencing (WGS), were included and analysed by MALDI-TOF MS. To take peak reproducibility into account, ethanol/formic acid extraction and other steps of the protocol were conducted in triplicate. Twenty-seven spectra were generated per isolate, and spectra were visually inspected to determine discriminatory peaks. The presence or absence of these was recorded in a peak scheme.Nine discriminatory peaks were identified. A characteristic pattern of these could distinguish between the three major WGS groups: WGS I, WGS II and WGS III. Only one of 38 isolates belonging to WGS I, WGS II or WGS III was misclassified. However, ten of the 17 isolates not belonging to WGS I, II or III displayed peak patterns indistinguishable from those of the outbreak strain.Using visual inspection of spectra, MALDI-TOF MS typing proved to be useful in differentiating three VREfm outbreak clones from each other. However, as non-outbreak isolates could not be reliably differentiated from outbreak clones, the practical value of this typing method for VREfm outbreak management was limited in our setting.