Improved Differentiation of Streptococcus pneumoniae and Other S. mitis Group Streptococci by MALDI Biotyper Using an Improved MALDI Biotyper Database Content and a Novel Result Interpretation Algorithm

Abstract

Reliable distinction of <i>Streptococcus pneumoniae</i> and viridans group streptococci is important because of the different pathogenic properties of these organisms. Differentiation between <i>S. pneumoniae</i> and closely related <i>Sreptococcus</i><i>mitis</i> species group streptococci has always been challenging, even when using such modern methods as 16S rRNA gene sequencing or matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. In this study, a novel algorithm combined with an enhanced database was evaluated for differentiation between <i>S. pneumoniae</i> and <i>S. mitis</i> species group streptococci. One hundred one clinical <i>S. mitis</i> species group streptococcal strains and 188 clinical <i>S. pneumoniae</i> strains were identified by both the standard MALDI Biotyper database alone and that combined with a novel algorithm. The database update from 4,613 strains to 5,627 strains drastically improved the differentiation of <i>S. pneumoniae</i> and <i>S. mitis</i> species group streptococci: when the new database version containing 5,627 strains was used, only one of the 101 <i>S. mitis</i> species group isolates was misidentified as <i>S. pneumoniae</i>, whereas 66 of them were misidentified as <i>S. pneumoniae</i> when the earlier 4,613-strain MALDI Biotyper database version was used. The updated MALDI Biotyper database combined with the novel algorithm showed even better performance, producing no misidentifications of the <i>S. mitis</i> species group strains as <i>S. pneumoniae</i> All <i>S. pneumoniae</i> strains were correctly identified as <i>S. pneumoniae</i> with both the standard MALDI Biotyper database and the standard MALDI Biotyper database combined with the novel algorithm. This new algorithm thus enables reliable differentiation between pneumococci and other <i>S. mitis</i> species group streptococci with the MALDI Biotyper.