Evaluation of Isothermal Target and Probe Amplification (iTPA) for the Detection of Mycobacterium Tuberculosis

This study compared the diagnostic power of isothermal target and probe amplification (iTPA) with the existing real-time PCR for the detection of Mycobacterium tuberculosis (MTB). The two molecular methods were performed using DNA extracted directly from lower respiratory tract samples, not from the culture broth. A total of 174 non-consecutive patients with suspected pulmonary tuberculosis were enrolled in this study. Acid-fast bacilli (AFB) stain and liquid culture with the BACTEC MGIT 960 system (Becton Dickinson Diagnostic, USA) were performed. Real-time PCR and iTPA methods were performed with the AdvanSure TB/NTM TaqMan assay (LG Lifescience, Korea) and the RapiDx® MTB test (RapleGene, Korea). Among 174 patients, 49 of 52 isolates were identified as MTB and 3 of 52 isolates were identified as non-tuberculous mycobacteria NTM. Based on the culture results, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 95.9%, 90.1%, 81.3%, and 98.2% for iTPA, and 95.7%, 91.0%, 80.4%, and 98.2% for real-time PCR, respectively. The agreement of iTPA was 83.0% with the AFB stain, 92.4% with the MGIT culture, and 94.2% with real-time PCR. Disagreement between the two molecular methods occurred in 10 patients. This study is the first to report the evaluation of iTPA conducted from direct specimens. Both iTPA and real-time PCR proved to be rapid, sensitive, and specific tools for the detection of MTB in clinical samples. The iTPA method for the MTB detection revealed a high concordance rate with real-time PCR.