alexa Identification of pathogenic microorganisms directly from positive blood vials by matrix-assisted laser desorption ionization time of flight mass spectrometry.
Chemical Engineering

Chemical Engineering

Mass Spectrometry & Purification Techniques

Author(s): Nonnemann B, Tvede M, Bjarnsholt T

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Abstract Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) is a promising and fast method for identifying fungi and bacteria directly from positive blood cultures. Various pre-treatment methods for MALDI-TOF MS identification have been reported for this purpose. In-house results for identification of bacterial colonies by MALDI-TOF MS using a cut-off score of 1.5 did not reduce the diagnostic accuracy compared with the recommended cut-off score of 1.8. A 3-month consecutive study of positive blood cultures was carried out in our laboratory to evaluate whether the Sepsityper™ Kit (Bruker Daltonics) with Biotyper 2.0 software could be used as a fast diagnostic tool for bacteria and fungi and whether a 1.5 cut-off score could improve species identification compared with the recommended score of 1.8. Two hundred and fifty-six positive blood vials from 210 patients and 19 blood vials spiked with fungi were examined. Using the cut-off score of 1.8, 81\% Gram-negative bacteria were identified to the species level compared to 84\% using a cut-off score of 1.5. For Gram-positive bacteria 44\% were identified to the species level with a cut-off of 1.8 compared to 55\% with the value of 1.5. The overall identification rate was 63\% (cut-off 1.5) and 54\% (cut-off 1.8). Seventy-seven per cent of fungal species were identified with both log scores. MALDI-TOF MS was in this study found to be a powerful tool in fast diagnosis of Gram-negative bacteria and fungi and to a lesser degree of Gram positives. Using 1.5 as cut-off score increased the diagnosis for both Gram-positives and -negatives bacteria. © 2013 APMIS. Published by John Wiley & Sons Ltd. This article was published in APMIS and referenced in Mass Spectrometry & Purification Techniques

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