title: Development of a rapid and simplified protocol for direct bacterial identification from positive blood cultures by using matrix assisted laser desorption ionization time-of- flight mass spectrometry.
abstract: BACKGROUND
  Bloodstream infections represent serious conditions carrying a high mortality and morbidity rate. Rapid identification of microorganisms and prompt institution of adequate antimicrobial therapy is of utmost importance for a successful outcome. Aiming at the development of a rapid, simplified and efficient protocol, we developed and compared two in-house preparatory methods for the direct identification of bacteria from positive blood culture flasks (BD BACTEC FX system) by using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOF MS). Both methods employed saponin and distilled water for erythrocyte lysis. In method A the cellular pellet was overlaid with formic acid on the MALDI TOF target plate for protein extraction, whereas in method B the pellet was exposed to formic acid followed by acetonitrile prior to placing on the target plate.
  
  
  RESULTS
  Best results were obtained by method A. Direct identification was achieved for 81.9 % and 65.8 % (50.3 % and 26.2 % with scores >2.0) of organisms by method A and method B, respectively. Overall concordance with final identification was 100 % to genus and 97.9 % to species level. By applying a lower cut-off score value, the levels of identification obtained by method A and method B increased to 89.3 % and 77.8 % of organisms (81.9 % and 65.8 % identified with scores >1.7), respectively. Using the lowered score criteria, concordance with final results was obtained for 99.3 % of genus and 96.6 % of species identifications.
  
  
  CONCLUSIONS
  The reliability of results, rapid performance (approximately 25 min) and applicability of in-house method A have contributed to implementation of this robust and cost-effective method in our laboratory.
authors.affiliation: Department of Medical Microbiology, St. Olavs Hospital, Trondheim University Hospital, Olav Kyrres gate 17, 7006, Trondheim, Norway. aleksandra.jakovljev@stolav.no.|Department of Laboratory Medicine, Children's and Women's Health, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. aleksandra.jakovljev@stolav.no.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Jakovljev
authors.affiliation: Department of Medical Microbiology, St. Olavs Hospital, Trondheim University Hospital, Olav Kyrres gate 17, 7006, Trondheim, Norway. kare.bergh@ntnu.no.|Department of Laboratory Medicine, Children's and Women's Health, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. kare.bergh@ntnu.no.
authors.forename: Kåre
authors.initials: K
authors.lastname: Bergh
mesh_terms: D016470:Bacteremia / Q000382:microbiology*; D001419:Bacteria / Q000145:classification / Q000254:growth & development / Q000302:isolation & purification*; D015373:Bacterial Typing Techniques / Q000379:methods*; D006801:Humans; D015203:Reproducibility of Results; D012503:Saponins / Q000378:metabolism; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D012503:Saponins