AUTHOR=Marín Mercedes , Cercenado Emilia , Sánchez-Carrillo Carlos , Ruiz Adrián , Gómez González Álvaro , Rodríguez-Sánchez Belén , Bouza Emilio 

TITLE=Accurate Differentiation of Streptococcus pneumoniae from other Species within the Streptococcus mitis Group by Peak Analysis Using MALDI-TOF MS

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00698

DOI=10.3389/fmicb.2017.00698

ISSN=1664-302X

ABSTRACT=<p>Despite the benefits of MALDI-TOF MS technology (Matrix-Assisted Laser Desorption-Ionization Time-Of-Flight Mass Spectrometry) reported worldwide and the continuous improving of the available databases, discrimination between <italic>Streptococcus pneumoniae</italic> and closely related species within the <italic>Streptococcus mitis</italic> group (SMG) using this methodology has been suboptimal. However, the accurate identification at the species level of this group of microorganisms is important for the appropriate management of infected patients. In this study, 216 SMG isolates -101 <italic>S. pneumoniae</italic> and 115 corresponding to 7 non-pneumococcal species within this group- were analyzed. All the isolates had been previously identified by conventional methods (optochin and bile solubility tests) and non-pneumococcal isolates were confirmed by sequence analysis (<italic>sodA</italic> and <italic>plys</italic> genes) when required. The isolates were also identified with the MALDI Biotyper 3.1 (Bruker Daltonics, Bremen, Germany) using an updated library containing 6,903 Main Spectra Profiles (MSPs). All the analyzed <italic>S. pneumoniae</italic> were correctly identified with MALDI-TOF MS at species level using the most updated database and all the non-pneumococcal SMG isolates were also identified at the group level. Several peaks (4,964.32, 6,888.90, and 9,516.46 m/z) have been found to be specific of <italic>S. pneumoniae</italic>, whilst a different set of peaks have proved to be present only in <italic>S. mitis</italic> (6,839.07 m/z) and <italic>S. oralis</italic> (5,297.61, 5822.53, and 6,839.07 m/z). Peak analysis allowed correct species assignment of 101/101 S. pneumoniae isolates (100%) and 102/105 <italic>S. mitis/oralis</italic> isolates (97.1%). Thus, the implementation of MALDI-TOF MS plus peak analysis for the identification of this group of microorganisms may provide precise species-level information that will allow the early implementation of directed antibiotic therapy.</p>