Validation of nanodiamond-extracted CFP-10 antigen as a biomarker in clinical isolates of Mycobacterium tuberculosis complex in broth culture media

With detonation nanodiamonds (DNDs) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS), we previously identified early secreted cell filtrate protein 10 (CFP-10) as a candidate Mycobacterium tuberculosis complex (MTC) biomarker. The performance of the CFP-10 biomarker was initially evaluated in relatively small mycobacterial samples (n = 42 samples) in our previous study. In this study, we conducted DND MALDI-TOF MS experiments to investigate the specificity and sensitivity of the MTC biomarker with 312 MTC and 52 nontuberculous mycobacteria (NTM) clinical samples. The frequency and intensity of the acquired CFP-10 mass-to-charge (m/z) peaks were checked with a program to validate that the singly and doubly charged CFP-10 antigen can be treated as a MTC biomarker. We confirmed that by detecting the singly charged species of CFP-10 antigen, the sensitivity and the specificity of MTC samples could reach 97.4% and 100% and no CFP-10 biomarker could be found in NTM samples. This indicates with CFP-10 biomarker it is easy to distinguish MTC from NTM. Besides, the observed intensity ratio of singly and doubly charged species of CFP-10 antigen was 3.3 ± 2.6 and the CFP-10 antigen could maintain good signal intensity for a week. Our results suggest that, with the DND MALDI-TOF mass spectrometry approach, CFP-10 antigen can be used as an early diagnosis biomarker in clinical practice.