Evaluation of the STANDARD M10 MDR-TB and MTB/NTM assays for the detection of Mycobacterium tuberculosis, rifampicin and isoniazid resistance, and nontuberculous mycobacteria in a low-incidence setting.

Abstract

Rapid detection is crucial for tuberculosis (TB) control. GeneXpert (Cepheid) is a widely used PCR system, known for its simplicity, random access, and point-of-care compatibility. SD BIOSENSOR recently introduced a similar system, STANDARD M10, including a Mycobacterium tuberculosis (MTB) and rifampicin (RIF) and isoniazid resistance (herein, MDR-TB) assay and an MTB/nontuberculous mycobacteria (NTM) assay. We evaluated these assays for the potential to replace the established Xpert MTB/RIF Ultra assay in a low-TB incidence setting. We analyzed 160 clinical respiratory samples (45 MTB-positive and 35 NTM-positive) and further 24 drug-resistant MTB, 30 mycobacterial species (2 MTB, 28 NTM), and 37 non-mycobacterial isolates. Compared with culture, clinical sensitivities and specificities for MTB detection were 88.9% (95% confidence interval [CI] = 76.1-95.6%) and 97.4% (CI = 92.3-99.4%) with Xpert Ultra, 88.9% (95% CI = 76.1-95.6%) and 98.3% (CI = 93.5-99.9%) with M10 MDR-TB, and 84.4% (CI = 70.9-94.4%) and 98.3% (CI = 93.5-99.9%) with M10 MTB/NTM, respectively. For NTM detection, M10 MTB/NTM showed sensitivity and specificity of 65.7% (CI = 49.1-79.2%) and 96.8% (CI = 91.8-99.0%). Compared with phenotypic drug susceptibility testing (DST), sensitivity and specificity for detecting RIF resistance were 100% (CI = 77.3-100%) and 95.6% (CI = 84.4-99.6%) with Xpert Ultra, and 100% (CI = 74.9-100%) and 95.5% (CI = 84.0-99.6%) with M10 MDR-TB. M10 MDR-TB showed 92.3% sensitivity (CI = 74.7-99.0%) and 100% specificity (CI = 87.3-100%) for detecting isoniazid resistance. All discrepancies in DST by PCR were concordant with whole-genome sequencing. While M10 MDR-TB demonstrated great potential as an alternative to Xpert Ultra, M10 MTB/NTM had limitations in NTM screening. Additionally, the M10 sputum pretreatment did not inactivate MTB efficiently, which should be considered in process risk assessment.

Importance: The molecular diagnostic STANDARD M10 system is highly analogous to the widely established GeneXpert system, which significantly increases the relevance of this evaluation study in the field of rapid detection of M. tuberculosis. To our knowledge, this is the first clinical evaluation describing the performance of the STANDARD M10 MDR-TB and MTB/NTM assays, including an extensive analytical specificity panel (inclusivity and exclusivity) for the detection of M. tuberculosis, drug resistance, and nontuberculous mycobacteria.