Performance assessment of the Bruker Biotyper MALDI-TOF MS for the identificationof difficult-to-identifyviridans group streptococci

Abstract

DifferentiatingStreptococcus pneumoniae among nonpneumococcal viridans group streptococci (VGS) is challenging in conventional laboratories. Therefore, we aimed to evaluate the performance of the latest Bruker Biotyper matrix-assisted laser desorption ionization-time of flightmass spectrometry (MALDI-TOF MS) system in identifying VGS by comparing the results to those of the specificgene sequencing approach. Clinical isolates were initially identifiedusing the BD Phoenix system to identify Streptococcus species. The optochin test was used to distinguish nonpneumococcal VGS from S. pneumoniae. The species of individual reference strains and clinical isolates were determined by comparing the sequences of the 16S rDNA, gyrB, sodA, groESL, or coaE genes with those in the GenBank sequence databases. We evaluated the performance of the Bruker Biotyper MALDI-TOF MS in VGS identificationusing two differentmachines with three databases. We collected a total of 103 nonpneumococcal VGS and 29 S. pneumoniae blood isolates at a medical center in northern Taiwan. Among these isolates, only seven could not be identifiedat the species level by the specificgene sequencing approach. We found that none of the nonpneumococcal VGS isolates were misidentifiedas pneumococci by the latest Biotyper system, and vice versa. However, certain strains, especially those in the mitis and bovis groups, could still not be correctly identified.The latest Bruker Biotyper 4.1 (DB_10833) showed significantimprovement in identifying VGS strains. However, a specificgene sequencing test is still needed to precisely differentiatethe species of strains in the mitis and bovis groups.