In-vivo expressed mycobacterial transcripts as diagnostic targets for pulmonary tuberculosis

The nucleic acid amplification tests (NAATs) such as Xpert MTB/RIF have transformed the TB diagnostic field by significantly increasing the case detection. However, newer improved diagnostic assays are still needed to meet the WHO targets to end TB. Present study is based on a novel approach of utilizing the in-vivo expressed specific mycobacterial transcriptomic biomarkers for the diagnosis of pulmonary tuberculosis (PTB). A total of 61 subjects were recruited including smear positive (smear+, n = 15), smear negative (smear-, n = 30) PTB patients and disease controls (n = 16). Transcripts of three mycobacterial genes Rv0986, Rv0971c and Rv3121 were analyzed using real time PCR (qRT-PCR) in sputum samples. qRT-PCR with Rv0986, Rv0971c and Rv3121 identified smear + PTB patients with 100 %, 78.6 % and 86.7 % sensitivity respectively. In smear- PTB patients, both Rv0986 and Rv0971c based qRT-PCR resulted in 63 %, sensitivity whereas Rv3121 identified these patients with ∼40 % sensitivity only. The sensitivity of the assay for smear-patients increased to 85 % when combinatorial analysis of qRT-PCR data for all the three genes was used. Thus, in-vivo expressed mycobacterial transcripts have promising potential as biomarkers for PTB diagnosis.