Evaluation of MALDI-TOF MS for identification of nontuberculous mycobacteria isolated from clinical specimens in mycobacteria growth indicator tube medium.

Nowadays, there is a rising worldwide incidence of diseases caused by nontuberculous mycobacteria (NTM) species, especially in immunocompromised patients and those with underlying chronic pulmonary diseases. Recently, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) became a method of choice for the identification of NTM species. The aim of this study was to evaluate MALDI-TOF MS for the identification of NTM isolates compared to the PCR-restriction enzyme analysis (PRA)-hsp65 method. In this study, a total of 152 NTM strains isolated from various clinical specimens were retrospectively analysed. MALDI-TOF MS successfully identified 148 (97.4%) of the 152 NTM isolates but failed to identify four (2.6%) of them. Bruker mycobacteria library gave spectral scores higher than 2.0 for 45 (29.6%) of NTM isolates, between 1.6 and 2.0 for 98 (64.5%) of NTM isolates, and lower than 1.6 for nine (5.9%) NTM isolates. The discordant results between MALDI-TOF MS and PRA-hsp65 analysis were confirmed by sequence analysis. In conclusion, MALDI-TOF MS is a technique capable of performing accurate, rapid, cost-effective, and easy identification of NTM isolates.