834. Evaluation of Matrix-Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) for the Identification of Microorganisms Directly from Positive Blood Culture Bottles
Session: Oral Abstract Session: Advances in Diagnostics
Saturday, October 22, 2011: 9:15 AM
Room: 151AB
Background: Diagnosis of bacteremia relies on initial culture in liquid media, followed by identification of the organism by subculture and biochemical testing.  Gram stain result and morphology can be reported within minutes of blood culture positivity, however full identification requires 24-72 hrs or longer.  We evaluated the MALDI Biotyper (Bruker Daltonics, Billerica, MS), coupled with the Sepsityper kit (Bruker), to identify bacteria directly from positive blood culture bottles.

Methods: 129 positive blood cultures from BACTEC Plus Aerobic/F and Lytic/10 Anaerobic/F bottles (BD, Sparks, MD) were analyzed.  One mL of culture was combined with lysis buffer and centrifuged.  The pellet was resuspended in wash buffer, centrifuged, and then extracted using ethanol/formic acid.  One µL of the extract was analyzed in duplicate using the Biotyper. The results were compared to routine biochemical identification methods.

Results: Of the 129 cultures analyzed, 81 contained gram-positive bacteria (GPB), 31 contained gram-negative bacteria (GNB), 5 contained yeast, and 12 were polymicrobial.  The Biotyper produced “acceptable” identifications (score >1.7) for 79.0% GPB cultures.  Four cultures contained Streptococcus mitis group organisms, which were identified as S. pneumoniae by the Biotyper due to near identical protein profiles.  Excluding these cultures, the Biotyper was 94.7% concordant with routine identification methods to genus and species.  Analysis of the 2 isolates producing discrepant results supported the Biotyper identification.  The Biotyper produced “acceptable” identifications for 100% of GNB cultures.  Concordance with routine identification methods was 100% to genus and 96.8% to species for GNB.  8 of 12 polymicrobial cultures (75%) had one organism correctly identified by the Biotyper.  Time from culture positivity to identification using routine methods ranged from 19.2 hrs (S. aureus) to 128.5 hrs (S. lugdunensis).  Time to identification for any isolate using the Biotyper/Sepsityper kit was 30 min

Conclusion: Biotyper/Sepsityper kit enables accurate identification of GPB and GNB from positive blood culture bottles within 30min.  This rapid identification could significantly impact patient management and antibiotic therapy.

Subject Category: D. Diagnostic microbiology

Blake Buchan, PhD1 and Nathan Ledeboer, PhD, D(ABMM)1,2, (1)Department of Pathology, Medical College of Wisconsin, Milwaukee, WI, (2)Dynacare Laboratories, Milwaukee, WI


B. Buchan, None

N. Ledeboer, Bruker Daltonics: Research Relationship, Research materials

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.