The accuracy of Mycobacterium tuberculosis complex identification using cording observation with mpt64 antigen as the reference standard.

Serpentine cording is a Mycobacterium tuberculosis complex (MTBC) specific colony morphology in liquid culture formed by outer mycomembrane component intracolonic interaction. This structure has the potential to streamline tuberculosis microbiology detection and potentially be used as a solo identification biomarker. This study assessed the sensitivity and specificity of cording-based identification compared to the presence of MPT64 antigen, by immunochromatography test or gene sequencing, as the reference standard for MTBC identification from culture. Direct cording observation by Microscopic Observation Drug Susceptibility (MODS) Assay was performed on 3426 screened TB suspects. As many as 1694 isolates were confirmed as MTBC and forty isolates as NTM (Non-Tuberculous Mycobacteria) only by cording visibility. Twelve pseudo-cording isolates were observed. Cording-based identification yields 100 % sensitivity and 76.9 % (95 % CI: 65.5 - 88.4) specificity. This study highlights the possibility of using cording as an MTBC identification biomarker after overcoming the pseudo-cording and mutation in MPT64 antigen.