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Evaluation of the Bruker MALDI Biotyper for identification of Gram-positive rods - development of a diagnostic algorithm for the clinical laboratory


Schulthess, Bettina; Bloemberg, Guido V; Zbinden, Reinhard; Böttger, Erik C; Hombach, Michael (2014). Evaluation of the Bruker MALDI Biotyper for identification of Gram-positive rods - development of a diagnostic algorithm for the clinical laboratory. Journal of Clinical Microbiology, 52(4):1089-1097.

Abstract

Reported MALDI-TOF MS identification rates of Gram-positive rods (GPR) are low compared to identification rates of Gram-positive cocci. In this study, three sample preparation methods were compared for MALDI-TOF MS identification of 190 well-characterized GPR strains: direct transfer, direct transfer-formic acid preparation, and ethanol-formic acid extraction. Using the interpretation criteria recommended by the manufacturer, identification rates were significantly higher for direct transfer-formic acid preparation and ethanol-formic acid extraction than for direct transfer. Reducing the species cutoff from 2.0 to 1.7 significantly increased species identification rates. In a subsequent prospective study, 215 clinical GPR isolates were analyzed by MALDI-TOF MS, and compared to identification using conventional methods, with discrepancies being resolved by 16S rRNA and rpoB gene analysis. Using the direct transfer-formic acid preparation and a species cutoff of 1.7, congruence on genus and species level of 87.4% and 79.1%, respectively, was achieved. In addition, the rate of non-identified isolates dropped from 12.1% to 5.6% when using an extended database, i.e. the Bruker database amended by reference spectra of the 190 GPR of the retrospective study. Our data demonstrate three ways to improve GPR identification by the MALDI Biotyper: optimization of sample preparation using formic acid, reduction of cutoff scores for species identification, and expansion of the database. Based on our results, we suggest an identification algorithm for the clinical laboratory combining MALDI-TOF MS with nucleic acid sequencing.

Abstract

Reported MALDI-TOF MS identification rates of Gram-positive rods (GPR) are low compared to identification rates of Gram-positive cocci. In this study, three sample preparation methods were compared for MALDI-TOF MS identification of 190 well-characterized GPR strains: direct transfer, direct transfer-formic acid preparation, and ethanol-formic acid extraction. Using the interpretation criteria recommended by the manufacturer, identification rates were significantly higher for direct transfer-formic acid preparation and ethanol-formic acid extraction than for direct transfer. Reducing the species cutoff from 2.0 to 1.7 significantly increased species identification rates. In a subsequent prospective study, 215 clinical GPR isolates were analyzed by MALDI-TOF MS, and compared to identification using conventional methods, with discrepancies being resolved by 16S rRNA and rpoB gene analysis. Using the direct transfer-formic acid preparation and a species cutoff of 1.7, congruence on genus and species level of 87.4% and 79.1%, respectively, was achieved. In addition, the rate of non-identified isolates dropped from 12.1% to 5.6% when using an extended database, i.e. the Bruker database amended by reference spectra of the 190 GPR of the retrospective study. Our data demonstrate three ways to improve GPR identification by the MALDI Biotyper: optimization of sample preparation using formic acid, reduction of cutoff scores for species identification, and expansion of the database. Based on our results, we suggest an identification algorithm for the clinical laboratory combining MALDI-TOF MS with nucleic acid sequencing.

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31 citations in Scopus®
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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Medical Microbiology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Date:2014
Deposited On:19 Mar 2014 13:30
Last Modified:05 Apr 2016 17:41
Publisher:American Society for Microbiology
ISSN:0095-1137
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1128/JCM.02399-13
PubMed ID:24452159

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