title: Direct Identification and Antimicrobial Susceptibility Testing of Bacteria From Positive Blood Culture Bottles by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry and the Vitek 2 System.
abstract: BACKGROUND
  We evaluated the reliability and accuracy of the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) bacterial identification and Vitek 2 antimicrobial susceptibility testing (AST) for bacteria from positive blood culture bottles.
  
  
  METHODS
  Direct identification and AST were performed in parallel to the standard methods in monomicrobial positive blood culture bottles. In total, 254 isolates grown on aerobic and/or anaerobic bottles were identified with MALDI-TOF Vitek MS (bioMérieux, France), and 1,978 microorganism/antimicrobial agent combinations were assessed. For isolates from anaerobic bottles, an aliquot of the culture broth was centrifuged, washed, and filtered through a nylon mesh. For isolates from aerobic/pediatric bottles, a lysis step using 9.26% ammonium chloride solution and 2% saponin solution was included.
  
  
  RESULTS
  The overall correct identification rate was 81.8% (208/254) and that for gram-positive/gram-negative isolates was 73.9%/92.6%, respectively, and it was 81.8%, 87.6%, and 57.9% for isolates from aerobic, anaerobic, and pediatric bottles, respectively. Identification was not possible in 45 cases, and most of these isolates were streptococci (N=14) and coagulase-negative staphylococci (N=11). Misidentification occurred only in one case. Compared with standard methods, direct AST showed 97.9% (1,936/1,978) agreement with very major error of 0.25%, major error of 0.05%, and minor error of 1.8%.
  
  
  CONCLUSIONS
  This simple and cost-effective sample preparation method gives reliable results for the direct identification and AST of bacteria. For the identification of streptococci and coagulase-negative staphylococci, the method should be further improved.
authors.affiliation: Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Sung Jin
authors.initials: SJ
authors.lastname: Jo
authors.affiliation: Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Kang Gyun
authors.initials: KG
authors.lastname: Park
authors.affiliation: Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Kyungja
authors.initials: K
authors.lastname: Han
authors.affiliation: Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Dong Jin
authors.initials: DJ
authors.lastname: Park
authors.affiliation: Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea. yjpk@catholic.ac.kr.
authors.forename: Yeon-Joon
authors.initials: YJ
authors.lastname: Park
mesh_terms: D000328:Adult; D000643:Ammonium Chloride / Q000737:chemistry; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002648:Child; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000302:isolation & purification* / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D011933:Reagent Kits, Diagnostic; D012503:Saponins / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000890:Anti-Infective Agents; D011933:Reagent Kits, Diagnostic; D012503:Saponins; D000643:Ammonium Chloride
keywords: Direct identification; MALDI-TOF MS; Positive blood culture; Vitek 2; Vitek MS