Evaluation of MALDI Biotyper Mycobacteria Library for Identification of Nontuberculous Mycobacteria

The Bruker Biotyper matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) platform was assessed on its ability to accurately identify 314 nontuberculous mycobacteria (NTM) representing 73 species. All NTM isolates, representing 183 rapidly growing and 131 slowly growing organisms, were previously identified by Sanger DNA sequencing of the full-length 16S rRNA gene, and region V of the rpoB gene. An optimized version of the Bruker bead-beating procedure for protein extraction of NTM isolates was used to ensure high quality spectra for all NTM isolates, including less frequently encountered species. NTM spectra were analyzed using Bruker's research use only, Mycobacteria Library v6.0, supplemented by the MicrobeNet database. Identification of NTM by MALDI-TOF had an accuracy of 94% (296/314). The identification accuracy for rapidly growing mycobacteria was higher at 99% (182/183) than it was for slowly growing mycobacteria at 87% (114/131). While MALDI-TOF performed well against Sanger sequencing of the 16S rRNA gene alone, there were 11 species that required additional sequencing of rpoB. Most discrepancies between MALDI-TOF and sequencing results are likely due to underrepresentation of some species in the libraries used. Overall, the results of this study support Bruker's MALDI-TOF platform as an accurate and reliable method for the identification of NTM.