Comparison between Vitek MS, Bruker Biotyper, Vitek2, and API20E for differentiation of species of the genus Raoultella

Rapid and reliable identification of microorganisms in the clinical laboratory is essential for an early and accurate diagnosis guiding timely therapy. However, conventional methods are sometimes unreliable and show controversial outcomes. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been reported as a rapid and reliable method for identification of bacteria and fungi isolated from clinical samples. Members of the genus Raoultella are increasingly recognized as clinically relevant. There are difficulties in their identification at the species level since sequencing the 16S rRNA or the rpoB genes does not show conclusive results. The aim of this study has been to compare two MALDI-TOF MS systems (Vitek MS and Bruker Biotyper) with Vitek2 and API20E systems for differentiation of Raoultella species. A collection of 97 clinical isolates of Raoultella species was identified with Vitek MS, in parallel with Vitek2 and API, and finally with Bruker Biotyper. Among the two most widely used MALDI-TOF MS platforms, results obtained with Vitek MS were slightly superior to those obtained with the Bruker Biotyper system, with sensitivities and specificities of 98.9/57.9% and 98.8/37.0%, respectively. The current commercial phenotypic identification systems are not optimized for the identification of Raoultella species. Our results indicate that MALDI-TOF-based identification is more accurate and sensitive than that provided by phenotypic methods.