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Performance of a Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry System for the Identification of Bacterial Isolates in the Clinical Routine Laboratory by Ulrich Eigner, Martin Holfelder, Klaus Oberdorfer, Ulrike Betz-Wild, Daniela Bertsch, Anne-Marie Fahr

Background: Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS) has emerged as a new tool for the fast and reliable identification of microorganisms. We evaluated the performance of a MALDI-TOF MS-system for the identification of various clinical isolates in the routine microbiology setting.
Material and Methods: For the evaluation study a set of 1116 bacterial isolates were collected in the routine microbiology laboratory. Additonally 108 isolates of strain culture collections (ATTC, DSMZ) were utilized. Identification of the bacterial isolates was perfomed with a Microflex LT mass spectrometer in combination with the MALDI-Biotyper 2.0 software (Bruker Daltonik GmbH, Bremen, Germany). The results of the MALDI-TOF MS were compared to phenotypic bacterial identification systems used in our routine laboratory. Discrepancies were resolved by 16 S rDNA-sequencing.
Results: Of the 108 reference strains tested, 101 (93,5%) were correctly identified to species level. Overall, 1062 (95,2%) of the 1116 strains collected in the routine laboratory were correctly identified with the MALDI-Biotyper. Accuracy for the identification of Enterobacteriaceae, non-fermenting gram-negative rods, staphylococci, enterococci and streptococci with the MALDI-Biotyper was 95,5 %, 79,7%, 99,5 %, 100% and 93,7 %, respectively. Results were available in 12 minutes for direct smear and in 20 min with an extraction method.
Conclusions: The MALDI-TOF method proves to be a fast and reliable method for the identification of the most important bacterial isolates in the clinical laboratory.

DOI: Clin. Lab. 2009;55:289-296