title: Matrix-assisted laser desorption/ionization-time of flight mass spectrometry identification of large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Clinical Microbiology, Herlev Hospital, University of Copenhagen , Herlev , Denmark.
authors.forename: Christian Salgård
authors.initials: CS
authors.lastname: Jensen
authors.forename: Casper
authors.initials: C
authors.lastname: Dam-Nielsen
authors.forename: Magnus
authors.initials: M
authors.lastname: Arpi
mesh_terms: D015373:Bacterial Typing Techniques / Q000379:methods*; D006801:Humans; D012336:RNA, Ribosomal, 16S; D065288:Serogroup; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013290:Streptococcal Infections / Q000097:blood / Q000175:diagnosis / Q000382:microbiology; D013291:Streptococcus / Q000145:classification* / Q000302:isolation & purification*; D013297:Streptococcus pyogenes / Q000145:classification / Q000302:isolation & purification
chemical_list: D012336:RNA, Ribosomal, 16S
keywords: Beta-hemolytic streptococci; MALDI-ToF; S. canis; S. dysgalactiae; S. pyogenes