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Rapid identification of bacteria from positive blood culture bottles by MALDITOFMS fingerprinting

Abstract number: P1791

Christner M., Rohde H., Wolters M., Sobottka I., Wegscheider K., Aepfelbacher M.

Objective: To establish and evaluate a method for rapid identification of bacteria from positive blood culture bottles using MALDI-TOF mass spectrometry.

Methods: Bacteria were isolated from positive BACTEC blood culture bottles by differential centrifugation and prepared for mass spectrometry fingerprinting by formic acid extraction. Spectrum acquisition and identification was performed with a microflex LT mass spectrometer and the MALDI Biotyper 2.0 software from Bruker. Reference identification was established from agar subcultures using well-proven biochemical and molecular typing methods.

Results: During the study period a total of 304 positive aerobic and anaerobic blood culture bottles from our clinical microbiology laboratory were investigated. Samples that grew yeast (8) or showed no sign of microbial growth by conventional processing (3) were excluded from further analysis. Isolates from the remaining study samples constituted a representative collection of bloodstream pathogens. Results from direct mass spectrometry fingerprinting matched reference identification for 262 of 277 monobacterial and 13 of 16 polymicrobial samples. A second isolate was correctly recognized in 4 of 16 mixed cultures (Gram stain: 2 of 16). The method worked equally well for aerobic and anaerobic culture bottles and was only slightly influenced by culture age. Misidentifications mostly resulted from insufficient bacterial numbers after sample preparation and were almost exclusively limited to Gram-positive isolates. Incorrect direct identification results could be reliably rejected by identification score cut-offs or tests for the bacterial origin of matched signals.

Conclusions: Combined with an efficient procedure for the preparation of bacteria from positive culture bottles, mass spectrometry fingerprinting is a reliable tool for the rapid identification of bloodstream pathogens. Compared to conventional identification from solid media subcultures, time to result is reduced by at least one workday. Providing species-level identification not later than one day after laboratory entry for 80% of our samples, the approach could facilitate targeted treatment optimizations within the critical phase of septic illness.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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