Identification of Streptococcus pseudopneumoniae and other mitis group streptococci using matrix assisted laser desorption/ionization- time of flight mass spectrometry

This study evaluated the ability of the MALDI-ToF MS from Bruker Daltonics to identify clinical Mitis-GroupStreptococcus isolates with a focus on Streptococcus pseudopneumoniae. The results were analyzed using the standard log(score) and the previously published list(score). Importantly, using the log(score) no misidentifications occurred and 27 of 29 (93%) S. pneumoniae and 27 of 30 (90%) S. oralis strains were identified, but only 1 of 31 (3%) S. pseudopneumoniae and 1 of 13 (8%) S. mitis strains were identified. However, our results show that 30 of 31 S. pseudopneumoniae strains had a S. pseudopneumoniae Main Spectral Profiles within the 3 best matches. Using the list(score) all S. oralis and S. pneumoniae strains were identified correctly, but list (score) misidentified 10 S. pseudopneumoniae and 5 S. mitis. We propose to use the log(score) for identification of S. pneumoniae, S. pseudopneumoniae, S. mitis and S. oralis, but for some strains additional testing may be needed. (c) 2021 Elsevier Inc. All rights reserved.