Diagnostic Performance of the STANDARD M10 MTB-RIF/INH Assay for Detection of Mycobacterium tuberculosis and Drug Resistance in Clinical Specimens

. (multidrug-resistant tuberculosis, MDR-TB) .MDR-TB 1 (isoniazid, INH) Objectives: Xpert MTB/RIF Ultra is the World Health Organization-recommended molecular diagnostic for Mycobacterium tuberculosis (MTB).However, it exclusively detects rifampicin (RIF) resistance and cannot identify resistance to other first-line drugs, such as isoniazid (INH) or fluoroquinolones.Additionally, some studies have reported reduced sensitivity in patients with a low bacterial burden (smear-negative TB).Methods: This study compared the performance of Xpert MTB/RIF Ultra with STANDARD M10 MTB-RIF/INH.The limit of detection (LOD) was assessed using MTB H37Rv strains, followed by analysis of 90 sputum samples from patients with suspected TB to evaluate MTB detection and RIF/INH resistance using both assays.Results: In LOD tests, Xpert MTB/RIF Ultra detected MTB at 1.0 10 1 CFU/mL with a "Trace detected" result and indeterminate RIF resistance, whereas STANDARD M10 MTB-RIF/INH identified both MTB and RIF/INH resistance at the same concentration.Among the 90 sputum samples, STANDARD M10 MTB-RIF/INH showed a higher MTB positivity rate than Xpert MTB/RIF Ultra (95.6% vs. 85.6%,P<0.05), with 8 discordant cases where Xpert MTB/RIF Ultra was negative but STANDARD M10 MTB-RIF/ INH was positive.This discordance was attributed to sensitivity of STANDARD M10 MTB-RIF/INH in detecting IS1081/IS6110, specifically, it identified IS1081 even in low-load samples where IS6110 was absent, outperforming Xpert MTB/RIF Ultra criteria (multi-copy probes Ct < 37, 2 rpoB probes Ct < 40).Conclusion: STANDARD M10 MTB-RIF/INH demonstrates sensitivity in low-burden sputum and enables simultaneous RIF/INH resistance detection, positioning it as a promising alternative to Xpert MTB/RIF Ultra for early TB diagnosis.Further multicenter validation is warranted.