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MALDI-TOF Mass Spectrometry as a Tool for Epidemiological Outbreak Analysis Can it Work?

Mutters NT, Burckhardt I and Heeg K

Background: Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF) provides fast and accurate identification of microorganisms. Several reports have speculated about its use in epidemiological typing. However, there is no systematic comparison with standard typing methods, such as pulsed-field gel electrophoresis (PFGE). This study evaluates the potential use of MALDI-TOF for the analysis of suspected outbreaks of vancomycin-resistant enterococci (VRE), compared to PFGE.

Methods: During a suspected outbreak of VRE, including five patients, on an intensive care unit, all isolates were analyzed by PFGE as well as by MALDI-TOF. A series of 24 spectra for each extracted isolate were created. Obtained spectra were smoothed, baseline corrected and calibrated. Subsequently, main spectra (MSP) were created using a Microflex mass spectrometer (Bruker-Daltonik) and the MALDI Biotyper 3.0. Mass peaks were compared manually; a dendrogram was automatically generated. All isolates were tested in triplicate to assess measurement fluctuations.

Results: Analysis of the MSP mass peaks and the dendrogram could clearly identify three different strains which were in agreement with the PFGE. Two clusters, reflecting four isolates and two occurred transmissions, were clearly identified. Measurement fluctuations did not affect the strain typing.

Conclusions: MALDI-TOF provided results concordant to PFGE and that in a fraction of time and costs. However, Bruker's algorithm for automated dendrogram creation is partly consisting of identification log scores making its resolution too low for exact typing analysis. Hence, fully automated analysis is not possible. However, the obtained results show some potential for the use of MALDI-TOF as an epidemiological tool for future outbreak management.