Abstract
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 (bioMerieux, 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 ® 2 system and by Kirby Bauer Method. 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. DOI: 10.21276/APALM.1212
Highlights
IntroductionThe presence of microorganisms in the blood or bloodstream infections (BSI), confirmed by a positive culture [1, 2], is a major cause of morbidity and mortality throughout the world . [3,4,5,6,7] During the period from 2000 to 2010, mortality from septicemia grew by 17% [8] and recent reports still show mortality to range from 34 to 52% [9].Microorganisms enter the bloodstream through various portals, including dissemination from a previous or concomitant infection and access via surgical sites, intravenous catheters, and other vascular access devices [10, 11]
Out of 124 positive blood samples included in this study, 70 were collected and inoculated in BD BACTECTM Plus Aerobic/F culture vials and incubated in the automated system BD BACTECTM FX, whereas 54 samples were collected and inoculated in Oxoid Signal Blood Culture System Medium (OXOID S.p.A.). Within these selected positive blood cultures, 60 Grampositive, 60 Gram-negative and 4 yeasts were correctly identified with MALDI-TOF system by LysisCentrifugation Method (LCM): 123 isolates were identified to the species level and 1 isolate was identified to the genus level
The identified microorganisms were analyzed for direct antimicrobial susceptibility testing by disc diffusion plate (Kirby Bauer Method) and by microdilution method AST by Vitek®2
Summary
The presence of microorganisms in the blood or bloodstream infections (BSI), confirmed by a positive culture [1, 2], is a major cause of morbidity and mortality throughout the world . [3,4,5,6,7] During the period from 2000 to 2010, mortality from septicemia grew by 17% [8] and recent reports still show mortality to range from 34 to 52% [9].Microorganisms enter the bloodstream through various portals, including dissemination from a previous or concomitant infection and access via surgical sites, intravenous catheters, and other vascular access devices [10, 11]. Bloodstream infections can be caused by a wide variety of microorganisms, commonly Escherichia coli, Klebsiella spp., Staphylococcus aureus, Enterococcus spp. and yeast. These infections can lead to increased mortality, longterm disability, excess length of stay in hospitals, large additional costs for health systems, and high costs as well as loss of quality of life for patients and their families [7]. Rapid identification and the application of antimicrobial susceptibility testing (AST) to microorganisms causing bloodstream infections is pivotal to guide antimicrobial therapy , [12] helping to reduce the detection time of the antimicrobial treatment and improving patient response. France) and by disc diffusion plate (Kirby Bauer Method) and 2) analyze the accuracy of these combined methods
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