A simplified extraction method reduces the processing time for proteomic identification of nontuberculous...

The identification of nontuberculous mycobacteria (NTM) by proteomic procedures has improved in the last few years. Strains from different geographical locations differ in their proteomic patterns, limiting the applicability of general databases for accurate identifications.

We have optimized an alternative extraction protocol to Myco-Ex, and MBT, the protocols recommended by Bruker Daltonics, the manufacturer of MALDI Biotyper, a Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) system. 120 clinical isolates, one environmental strain (Mycobacterium canariasense) and 7 quality controls were tested from the Spanish Society of Clinical Microbiology and Infectious Diseases (SEIMC). All strains were also sent to the Laboratory of Mycobacteria belonging to the National Spanish Reference Center (Instituto de Salud Carlos III), that uses several molecular methods for mycobacterial identification. The proteomic extraction method includes a single extraction/inactivation formic acid step. 30 NTM strains were analyzed to certify the biosafety of the procedure, testing their viability after this procedure.

The score ranges of the isolates were 1.61-2.16 (mean 1, 84) for the 88 isolates of the slow growing mycobacteria group (SGM) and 1.66-2.33 (mean 2.06) for the 40 isolates of the rapid growing mycobacteria group (RGM). Isolates exposed to formic acid were incubated for 8 weeks and growth was observed in neither the clinical isolates nor the controls.

We have developed a simpler and faster procedure for the proteomic identification of nontuberculous mycobacteria (MALDI-TOF) retaining significant scores without compromising biosafety.