[1620] Identification of Anaerobic Bacteria Using MALDI-TOF MS Bruker Biotyper System

Yen-Michael S Hsu, Carey-Ann D Burnham. Washington University School of Medicine, Saint Louis, MO

Background: Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) has emerged as a method for identifying clinically relevant microorganisms. To date, data on the performance of MALDI-TOF MS for identification of anaerobic organisms is scarce. The objective of this study was to evaluate the performance of MALDI-TOF MS for identification of anaerobic bacteria using the direct spotting (DS) method, with and without a direct formic acid (FA) overlay.
Design: A total of 102 anaerobic bacteria, including 87 clinical isolates and 15 stock organisms, were tested using the Bruker Microflex LT with Biotyper 3.0 software. All isolates were tested in quadruplicate; in duplicate by DS and in duplicate using DS with a 1 uL FA overlay (DS+FA). The MALDI-TOF MS identification was compared to the phenotypic identification from the clinical laboratory. Full length 16S rDNA gene sequencing was used for discrepant analysis, and taken as the gold standard. A full FA extraction was performed on isolates with a score of <2.000.
Results: For analysis, the isolates were divided into 3 groups: Gram-negative bacilli (GNB), Gram-positive bacilli (GPB), and Gram-positive cocci (GPC). For all groups, the FA overlay (DS+FA) improved the average score and reduced the frequency of unidentified isolates.

Overall, 91%(DS)/99%(DS+FA) of isolates were correctly identified to Genus level (score of ≥1.700), and 72%(DS)/86%(DS+FA) of isolates were correctly identified to species level (score of ≥2.000), without misidentifications by either method. For 8 of the 102 isolates (8%), a score of <2.000 was obtained by both DS and DS+FA methods using both the automatic or manual mode on MALDI-TOF MS. A complete FA extraction was performed on these 8 isolates, which yielded identification in only one case (a Gemella spp.).
Conclusions: MALDI-TOF MS with Biotyper 3.0 can accurately and rapidly identify clinically relevant anaerobic bacteria. DS with a FA overlay will enhance laboratory workflow by reducing the number of full FA extractions required. MALDI-TOF MS will improve turn-around-time for identification of clinically relevant anaerobes for a very low consumable cost.
Category: Infections

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 245, Monday Morning


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