Use of MALDI-TOF mass spectrometry to detect nosocomial outbreaks of Serratia marcescens and Citrobacter freundii
MALDI-TOF mass spectrometry (MS) may be used as a rapid typing method for nosocomial pathogens. Here, we evaluated MALDI-TOF MS for discrimination of hospital outbreak-related clusters of Serratia marcescens and carbapenemase-producing Citrobacter freundii. Thirty-three S. marcescens isolates collected from neonatal intensive care unit (NICU) patients, and 23 C. freundii isolates including VIM-positive isolates from a hospital colonization outbreak were measured by Vitek MS. Consensus spectra of each isolate were clustered using SARAMIS software. Genotyping was performed by whole-genome sequencing (WGS). First, a set of 21 S. marcescens isolates from 2014 with seven genotypes including three monoclonal clusters was used for the evaluation of MALDI-TOF typing. MS clustering was largely in agreement with genotyping results when the similarity cut-off for clonal identity was set on 90%. MALDI-TOF cluster analysis was then investigated for the surveillance of S. marcescens in the NICU in 2017 and demonstrated the introduction of new strains into the hospital and nosocomial transmissions. MS analysis of the C. freundii outbreak in 2016 revealed a monoclonal cluster of VIM-positive isolates and the separation of epidemiologically non-related VIM-positive and negative isolates. Two additional VIM-positive Citrobacter isolates from food samples were closely related to the large monoclonal cluster. WGS confirmed the MS results. MALDI-TOF MS may be used as a first-line typing tool for S. marcescens and C. freundii to detect transmission events in the hospital because isolates of an identical WGS type were grouped into the same MS cluster.
KeywordsSerratia marcescens Citrobacter freundii Typing MALDI-TOF Whole genome sequencing
We thank Sabine Trommer (Public Health Office Jena), Helke Dobermann, Mathias Pletz (Jena University Hospital), and their team of hygiene professionals for the excellent work during the C. freundii outbreak in 2016. We thank Wolfgang Stöckigt, Dietmar Schönherr, and Friedrich Dübler (bioMérieux) for technical support for the Vitek MS machine. We thank Ursula Keckvoet, Isabell Höfig, and Stefan Bletz (Institute of Hygiene, University Hospital Münster) for their skillful technical assistance during WGS.
This work was supported by a grant from the German Federal Ministry of Education and Research (BMBF, 13N13890).
Compliance with ethical standards
Because in this work a method for subtyping bacterial isolates was developed and the paper contains no patient data, research ethics committee approval was not required.
Conflict of interest
The authors declare that there are no conflicts of interest.
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