MALDI-TOF typing of Serratia marcescens, Klebsiella oxytoca, and Citrobacter freundii for fast discrimination of isolates during outbreaks

MALDI-TOF mass spectrometry (MS) was evaluated for strain-specific typing of Serratia marcescens, Klebsiella oxytoca VIM, and Citrobacter freundii VIM. The results were compared with next generation whole genome sequencing (WGS) analysis. A collection of 21 S. marcescens, 10 K. oxytoca, and 14 C. freundii isolates were sequenced by WGS using a MiSeq instrument (Illumina, San Diego, CA, USA) and Ridom SeqSphere software (Ridom GmbH, Münster, Germany). For MALDI-TOF analysis bacterial colonies were measured on a Vitek MS system (bioMerieux and clustered using SARAMIS software. Compared to WGS the resolution of MALDI-TOF spectra is lower but the data of this study suggest that MS analysis can be applied in a local setting as a screening method for the early identification of nosocomial outbreaks in high-risk wards.