Comparison of the Bruker Biotyper and Vitek MS Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry Systems for Identification of Mycobacteria Using Simplified Protein Extraction Protocols

Abstract

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has recently been described as a fast and inexpensive method for the identification of mycobacteria. Although mycobacteria require extraction prior to MALDI-TOF MS analysis, previously published protocols have been relatively complex, involving significant hands-on time and materials not often found in the clinical laboratory. In this study, we tested two simplified protein extraction protocols developed at the University of Washington (UW) and by bioMérieux (BMX) for use with two different mass spectrometry platforms (the Bruker MALDI Biotyper and the bioMérieux Vitek MS, respectively). Both extraction protocols included vortexing with silica beads in the presence of ethanol. The commercial Bruker database was also augmented with an in-house database composed of 123 clinical Mycobacterium strains. A total of 198 clinical strains, representing 18 Mycobacterium species, were correctly identified to the species level 94.9% of the time when extracted using the UW protocol and compared to the augmented database. The BMX protocol and Vitek MS system resulted in correct species-level identifications for 94.4% of these strains. In contrast, only 79.3% of the strains were identified to the species level by the nonaugmented Bruker database, although the use of a lower identification score threshold (>1.7) increased the identification rate to 93.9%, with two misidentifications that were unlikely to be clinically relevant. The two simplified protein extraction protocols described in this study are easy to use for identifying commonly encountered Mycobacterium species.

Rapid Detection of Vancomycin-Intermediate Staphylococcus aureus by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

“…One microliter of the final supernatant was spotted in duplicate onto a 96-well polished stainless steel target plate and overlaid with 1 l of a saturated solution of ␣-cyano-4-hydroxycinnamic acid in 50% acetonitrile and 2.5% trifluoroacetic acid (both from Bruker Daltonics, Billerica, MA). Spectra were acquired in a linear positive-ion mode at a laser frequency of 60 Hz across a mass/charge (m/z) ratio of 2,000 to 20,000 with a MicroFlex LT mass spectrometer (Bruker Daltonics) as described previously (19). For each spectrum, 240 laser shots in 40-shot steps from different areas of the sample spot were accumulated and analyzed (automatic mode, default settings).…”

Comparison of Sample Preparation Methods, Instrumentation Platforms, and Contemporary Commercial Databases for Identification of Clinically Relevant Mycobacteria by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

“…(8)(9)(10)(11). However, unlike most bacteria, which can be directly spotted onto a MALDI-TOF target plate, mycobacteria require inactivation and extraction steps prior to analysis, both for biosafety and for access to proteins in the cells.…”

MALDI-TOF MS Assessment to Identify Environmental Mycobacteria

“…Furthermore, the effect of microorganism inactivation by heat has been evaluated, and it has been shown that the quality of the spectrum decreases with increasing temperature [24]. It was also recently reported that the conditions of microorganism cultivation also influence the spectrum [25] [26]. However, in another study, the effect of culture age, chilling or freezing the lysates and freeze-thaw cycles did not have any impact on spectrum quality [27].…”