Utility of the MALDI-TOF MS method to identify nontuberculous mycobacteria

In comparison to the conventional real-time polymerase chain reaction method (PCR method) or the DNA-DNA hybridization method (DDH method), the utility of NTM identification by the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method has seldom been reported. In this study, 75 clinical NTM isolates from our hospital between April 2013 and July 2014 were identified and analyzed using PCR, DDH, and MALDI-TOF MS methods, and the results for the MALDI-TOF MS method were compared with the others. Identification at the species level was in agreement for 71 (94.5%) of the 75 isolates. For further details, identification was possible for 23 (95.8%) of 24 Mycobacterium avium, 11 (100%) of 11 Mycobacterium intracellulare, and 1 (50%) of 2 isolates mixed with M. avium and M. intracellulare. Mycobacterium ksansasii, Mycobacterium abscessus, Mycobacterium fortuitum, Mycobacterium gordonae, and Mycobacterium chelonae identified by DDH method were same result by MALDI-TOF MS. Additionally, Mycobacterium mucogenicum, which could not be identified by the DDH method, was identified by the MALDI-TOF MS method. However, two isolates identified as Mycobacterium terrae by DDH method could not be identified by the MALDI-TOF MS method and were determined to be Mycobacterium arupense by 16S ribosomal RNA (rRNA) sequence analysis. The present findings show that, for rare bacterial species, identification is sometimes not possible, but, in most cases, the results of identification by the MALDI-TOF MS method have a high concordance rate with the results of the PCR and DDH methods.