We evaluated the reliability and accuracy of the combined use of MALDI-TOF MS and classical ID VITEK2 to identify monomicrobial infection in blood culture bottles. In total, 70 consecutive positive blood cultures were included in this study. Positive blood culture bottles were subjected to Gram staining and subcultured on solid media. Isolates grown from such culture media were used for classical ID using VITEK2 system. In parallel, an aliquot was subjected to a lysing-centrifugation method and used for the identification with the MALDI-TOF system. Results evidenced the correct genus and species identification of 91.4 % of microorganisms responsible for bacteremia with an agreement to the species and the genus level. If compared with the standard method VITEK2, our simple and cost-effective sample preparation method would be very useful for rapid identification of microorganisms using blood culture bottles. In fact, the direct method showed rapid and reliable results, especially for the gram-negative group.

Background: Rapid identification and the application of antimicrobial susceptibility testing (AST) to microorganisms causing bloodstream infections is pivotal to guide antimicrobial therapy. This study aims to: 1) utilize the Lysis-Centrifugation Method (LCM) not only for identification of microorganisms from positive blood culture bottles, but also for direct AST full panel by Vitek ® 2 system (bioMérieux, Inc. France) and by disc diffusion plate (Kirby Bauer Method) and 2) analyze the accuracy of these combined methods.Methods: 124 mono-microbial positive blood culture bottles were included in this study. An aliquot was subjected to LCM and used for the identification by the MALDI-TOF System. Moreover the microbial pellet was used for direct AST testing full panel by VITEK Results: 123 isolates were correctly identified to the species level and 1 isolate was identified to the genus level. Comparing the two utilized AST methods, it was observed that Gram-positive isolates showed an agreement rate of 96.6% (58/60). Enterococcus faecalis was the only microorganism with a major error rate of 0.6% (2/324) related to erythromycin. Among the Gram-negative, the overall agreement rate was 93.3 (56/60). Klebsiella pneumoniae, Escherichia coli and Enterobacter spp. were the major cause of minor error rates (0.6%, 4/709) and major error rates (1.1%, 8/709). Among the yeasts, results showed an agreement rate of 100% (4/4). Conclusions:Our simple and cost-effective sample preparation method is very useful for rapid identification as well as AST of microorganisms directly from positive blood culture bottles in a clinical setting.