![Sample our Bioscience journals, sign in here to start your access, Latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5925/TOC-Subject-Sample-2021-Bioscience.jpg"})
Abstract
Background: The aim of this study was to investigate whether large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G can be adequately identified using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-ToF). Previous studies show varying results, with an identification rate from below 50% to 100%. Methods: Large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G isolated from blood cultures between January 1, 2007 and May 1, 2012 were included in the study. Isolates were identified to the species level using a combination of phenotypic characteristics and 16s rRNA sequencing. The isolates were subjected to MALDI-ToF analysis. We used a two-stage approach starting with the direct method. If no valid result was obtained we proceeded to an extraction protocol. Scores above 2 were considered valid identification at the species level. Results: A total of 97 Streptococcus pyogenes, 133 Streptococcus dysgalactiae, and 2 Streptococcus canis isolates were tested; 94%, 66%, and 100% of S. pyogenes, S. dysgalactiae, and S. canis, respectively, were correctly identified by MALDI-ToF. Discussion: In most instances when the isolates were not identified by MALDI-ToF this was because MALDI-ToF was unable to differentiate between S. pyogenes and S. dysgalactiae. By removing two S. pyogenes reference spectra from the MALDI-ToF database the proportion of correctly identified isolates increased to 96% overall. MALDI-ToF is a promising method for discriminating between S. dysgalactiae, S. canis, and S. equi, although more strains need to be tested to clarify this.
Acknowledgment
We thank Ane Glad for critical reading of the manuscript.
Declaration of interest: The authors declare no conflicts of interest. No funding was received.