Antimicrobial resistance classification using MALDI-TOF-MS is not that easy: lessons from vancomycin-resistant Enterococcus faecium

Matrix-assisted Laser-Desorption/Ionization Time-of-Flight mass spectrometry (MALDI-TOF MS) is a routinely applied technique to identify bacterial species. The acquired spectra show predominantly the molecular weights of ribosomal proteins. Once acquired, the spectra are compared with a database of either previously acquired spectra for which the organism is known or theoretical spectra based on predicted masses from sequence data, and identified based on identical peaks. Many efforts are undertaken to expand the information that can be extracted from these spectra to deduct further features regarding the antibiotic resistance phenotype or even the presence of virulence factors.