A novel isothermal amplification-based method to detect Mycobacterium tuberculosis complex

Mycobacterium tuberculosis (MTB) is the causative agent of pulmonary tuberculosis. Rapid and accurate diagnosis is crucial to tuberculosis control and prevention. A series of diagnostic methods has been available for MTB detection; however, new rapid, simple and affordable methods are needed. In this study, a multiple cross displacement amplification (MCDA)-based assay was developed to detect the IS6110 gene of the M. tuberculosis complex. Hydroxy naphthol blue (HNB), a colorimetric indicator, was used to detect amplification products. Amplification was carried out at a constant temperature (68°C) for only 40min, followed by direct determination of amplification products through observation of color variations. The entire detection procedure, from processing of specimens to reading of results, required only 85min. Moreover, this assay, hereafter designated MTB-MCDA-HNB, was able to detect as little as 1pg of DNA extracted from the Bacille Calmette-Guerin (BCG) strain of Mycobacterium bovis. No cross-reaction with nontuberculous mycobacteria (NTM) species was observed. Moreover, during testing of clinical samples, the sensitivity and specificity of MCDA results were 94.7% and 92.9%, respectively, when compared to results obtained using the Xpert MTB/RIF method. Therefore, the MTB-MCDA-HNB method developed in this study holds promise for application as an effective point-of-care test to detect M. tuberculosis.