New assay to diagnose and differentiate between Mycobacterium tuberculosis complex and nontuberculous mycobacteria

The purpose of the present study was to create a real-time PCR test system allowing simultaneous detection of nontuberculous mycobacteria (NTM) and Mycobacterium tuberculosis complex (MTBC) both in culture and sputum. NTM cultures (18 strains, 18 species), MTBC cultures (16 strains, 2 species) and non-mycobacterial microorganisms from the collection of the Central Research TB Institute (CTRI) were used for the preliminary evaluation of the test system. 301 NTM cultures from patients with mycobacteriosis were used to assess the sensitivity of the developed test system. Clinical respiratory samples (sputum) from 104 patients with mycobacteriosis, 3627 patients with tuberculosis and 118 patients with other lung diseases were used for diagnostic sensitivity and specificity testing. The specificity and sensitivity of the assay for MTBC was found to be 100% both in culture and sputum samples; for NTM, the specificity was 100% in culture and sputum, the sensitivity reached 100% in culture and 73.1% in sputum samples. Positive predictive value (PPV) and negative predictive value (NPV) of the assay for culture were both 100%, for clinical material 100% and 80.8%, respectively. The limit of detection at the probability of detection 95% (LoD95%) was estimated to be 16 cfu/ml for M. tuberculosis H37RV and 1200 cfu/ml for M. avium.