Identification of isolates of Mycobacterium spp. by MALDI-TOF mass spectrometry

Study objective: Matrix-assisted laser desorption/ionization- time-of-flight mass spectrometry (MALDI-TOF MS) has recently been widely used in diagnostic microbiological laboratories. It is a cheap and rapid method for the identification of bacteria and micromycetes. Apart from this purpose, it is also used for the detection of antibiotic resistance mechanisms. It has the potential to be extended for other purposes in microbiology. The aim of this study was to validate MALDI-TOF MS for the identification of mycobacteria. Material and methods: Thirty isolates of Mycobacterium spp. isolated in the Laboratory of Mycobacteriology of the Plzen University Hospital were included in the study. The isolates were identified to the species level using biochemical tests, gene probes, and sequencing of the gene encoding 16S rRNA. The identification by MALDI-TOF MS was performed with the use of silica beads. Strain identification by sequencing the gene encoding 16S rRNA was considered as the reference method. Results: MALDI-TOF MS correctly identified all isolates of Mycobacterium spp. (score range 1.461 - 2.168). The species identified were Mycobacterium tuberculosis (n= 5), Mycobacterium kansasii (n= 5), Mycobacterium avium (n= 6), Mycobacterium intracelullare (n= 3), Mycobacterium xenopi (n= 3), Mycobacterium gordonae (n= 1), Mycobacterium abscessus (n= 1), Mycobacterium kumamotonense (n= 2), Mycobacterium mantenii (n= 1), Mycobacterium lentiflavum (n= 1), Mycobacterium fortuitum (n= 1), and Mycobacterium scrofulaceum (n= 1). Conclusion: MALDI-TOF MS is a suitable tool for the routine identification of Mycobacterium spp. in laboratories using this method for the conventional identification of microbes.