Matrix-assisted laser desorption/ionization-time of flight mass spectrometry identification of large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G

• Published in: Infectious diseases (London, England) England), 2015-08, Vol.47 (8), p.575-579
• Main Authors: Jensen, Christian Salgård, Dam-Nielsen, Casper, Arpi, Magnus
• Format: Article
• Language: English
• Subjects: Bacterial Typing Techniques - methods; Beta-hemolytic streptococci; Humans; MALDI-ToF; RNA, Ribosomal, 16S; S. canis; S. dysgalactiae; S. pyogenes; Serogroup; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Streptococcal Infections - blood; Streptococcal Infections - diagnosis; Streptococcal Infections - microbiology; Streptococcus - classification; Streptococcus - isolation & purification; Streptococcus pyogenes - classification; Streptococcus pyogenes - isolation & purification
• ISSN: 2374-4235; 2374-4243
• DOI: 10.3109/23744235.2015.1043940

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.