title: Insufficient discriminatory power of MALDI-TOF mass spectrometry for typing of Enterococcus faecium and Staphylococcus aureus isolates.
abstract: MALDI-TOF mass spectrometry (MALDI-TOF MS) is increasingly used as a reliable technique for species identification of bacterial pathogens. In this study we investigated the question of whether MALDI-TOF MS can be used for accurate sub-differentiation of strains and isolates of two important nosocomial pathogens Enterococcus faecium and Staphylococcus aureus. For this purpose, a selection of 112 pre-characterized E. faecium isolates (clonal complexes CC2, CC5, CC9, CC17, CC22, CC25, CC26, CC92 altogether 52 multilocus sequence types) and 59 diverse S. aureus isolates (mostly methicillin resistant; CC5, CC8, CC22, CC30, CC45, CC398) were studied using a combination of MALDI-TOF MS and advanced methods of spectral data analysis. The strategy of MS data evaluation included manual peak inspection on the basis of pseudo gel views, unsupervised hierarchical cluster analysis and supervised artificial neural network (ANN) analysis. We were capable of differentiating patterns of hospital-associated E. faecium isolates (CC17) from other strains of E. faecium with 87% accuracy, but failed to identify lineage-specific biomarker peaks. For S. aureus pattern analyses we were able to confirm a number of signals described in previous studies, but often failed to identify biomarkers that would allow a consistent and reliable identification of phylogenetic lineages, clonal complexes or sequence types. Hence, the discriminatory power of MALDI-TOF MS was found to be insufficient for reliably sub-differentiating E. faecium and S. aureus isolates to the level of distinct clones or clonal complexes, such as assessed by MLST. Further, a comparison between peak patterns of susceptible and resistant isolates did not identify statistically relevant marker peaks linked to glycopeptide resistance determinants (vanA, vanB) in E. faecium, or the methicillin resistance determinant (mecA) in S. aureus.
authors.affiliation: Robert Koch Institute, Division Proteomics and Spectroscopy (ZBS 6), Berlin, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Lasch
authors.affiliation: Robert Koch Institute, Division Nosocomial Pathogens and Antimicrobial Resistances (FG13), Wernigerode Branch, Germany.
authors.forename: Carola
authors.initials: C
authors.lastname: Fleige
authors.affiliation: Robert Koch Institute, Division Proteomics and Spectroscopy (ZBS 6), Berlin, Germany.
authors.forename: Maren
authors.initials: M
authors.lastname: Stämmler
authors.affiliation: Robert Koch Institute, Division Nosocomial Pathogens and Antimicrobial Resistances (FG13), Wernigerode Branch, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Layer
authors.affiliation: Robert Koch Institute, Division Nosocomial Pathogens and Antimicrobial Resistances (FG13), Wernigerode Branch, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Nübel
authors.affiliation: Robert Koch Institute, Wernigerode Branch, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Witte
authors.affiliation: Robert Koch Institute, Division Nosocomial Pathogens and Antimicrobial Resistances (FG13), Wernigerode Branch, Germany. Electronic address: WernerG@rki.de.
authors.forename: Guido
authors.initials: G
authors.lastname: Werner
mesh_terms: D015373:Bacterial Typing Techniques / Q000379:methods*; D003428:Cross Infection / Q000382:microbiology; D016984:Enterococcus faecium / Q000737:chemistry* / Q000145:classification*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology; D006801:Humans; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013211:Staphylococcus aureus / Q000737:chemistry* / Q000145:classification*
keywords: Outbreak; Population analysis; Typing; VRE