Evaluation and clinical impact of MALDI Biotyper Mycobacteria Library v6.0 for identification of nontuberculous mycobacteria by MALDI-TOF mass spectrometry

Major challenges in the identification of non-tuberculous mycobacteria (NTM) by MALDI-TOF MS include protein extraction protocol and updating of the NTM database. The aim of this study was to evaluate MALDI Biotyper Mycobacteria Library v6.0 (Bruker Daltonics GmbH, Bremen, Germany) for identification of clinical NTM isolates and its impact on clinical management. NTM isolates cultivated from clinical samples in 101 patients were identified simultaneously by PCR-reverse hybridization (Hain Lifescience GmbH, Nehren, Germany) as a routinely used reference molecular method and using MALDI Biotyper Microflex LT/SH after protein extraction. Each isolate was applied to eight spots, and mean scores were used in analysis. MALDI-TOF MS obtained correct identification to the species level for 95 (94.06%) NTM isolates. The majority of correctly identified isolates (92/95; 96.84%) were identified with high-confidence score of ≥1.80 and only 3.16% (3/95) with a score of <1.80. Mean value ± SD of RGM NTM isolates (2.127 ± 0.172) was statistically significant higher in comparison to SGM NTM isolates (2.027 ± 0.142) with a p value of 0.007. In comparison to PCR-reverse hybridization, discordant identification results by MALDI-TOF MS were found in six (6/101; 5.94%) NTM isolates for which clinical data were analyzed. We demonstrated a high confidence NTM identifications using Mycobacterium Library v 6.0 on routine clinical isolates. This is the first study that analyzed MALDI-TOF MS identification results of NTM isolates in the context of clinical data, and it showed that MALDI-TOF MS with its updated databases could help clarify the epidemiology, clinical characteristics, and course of infections caused by less frequent NTM species.