Demographic characteristics and patient profile.

Background
Cross contamination and biosafety are concerns with the microscopic observation drug susceptibility assay. To address these issues, we modified the MODS technique in the current study.
Methodology/Principal findings
Two hundred and seventy-five samples were processed on LJ media and drug susceptibility was performed by the Indirect agar proportion method. A modified MODS test was done in tissue culture bottles. GenoType MTBDRplus assay was performed to detect the resistance and mutational pattern associated with the resistances. Sensitivity, specificity, positive predictive value, and negative predictive value for the detection of tuberculosis by modified MODS were 97.44%, 80.00%, 97.44%, and 80.00% respectively. The perfect agreement was seen between modified MODS and the Indirect agar proportion method for drug susceptibility testing of isoniazid (kappa = 0.923) and rifampicin (kappa = 1). The contamination rate, cost and TAT for modified MODS were less as compared to the solid media.
In the case of MDR-TB isolates S531L (66.66%) was the most prevalent mutation in the rpoB gene followed by S315T2 mutation (58.33%) and T8C (41.66%) in katG and inhA gene respectively. In hetero-resistant strains, C-15T mutation (37.50%) was the most common followed by A-16G (12.50%) in the inhA gene. In INH mono-resistant strains only two mutations were observed i.e., S-315T1(50%) and C-15T (50%) in the katG and inhA genes respectively.
Conclusions/Significance
Modified MODS proved to be cost-effective and user-friendly, with minimal risk to the handler and no cross-contamination between samples were observed. Hence, it can be used in low-income countries for early detection of tuberculosis and its resistance.

背景
交叉污染与生物安全是显微镜观察药物敏感性试验（Microscopic Observation Drug Susceptibility Assay，简称MODS）所面临的核心关切问题。为解决上述问题，本研究对MODS技术进行了改良。

方法学与主要结果
本研究采用吕文-约翰逊培养基（Lowenstein-Jensen Medium，简称LJ培养基）处理275份样本，通过间接琼脂比例法开展药物敏感性检测。改良MODS试验则在组织培养瓶中进行。此外，采用GenoType MTBDRplus试验检测结核分枝杆菌耐药性及其相关突变模式。改良MODS检测结核病的灵敏度、特异度、阳性预测值与阴性预测值分别为97.44%、80.00%、97.44%和80.00%。在异烟肼（isoniazid）与利福平（rifampicin）的药物敏感性检测中，改良MODS与间接琼脂比例法的检测结果具有极佳一致性（kappa值分别为0.923与1）。相较于固体培养基，改良MODS的污染率、检测成本与周转时间（Turnaround Time，简称TAT）均更低。

针对耐多药结核病（Multidrug-Resistant Tuberculosis，简称MDR-TB）分离株，rpoB基因中S531L突变最为常见（占比66.66%），其次为katG基因的S315T2突变（58.33%）与inhA基因的T8C突变（41.66%）。在异质性耐药菌株中，inhA基因的C-15T突变最为普遍（37.50%），其次为A-16G突变（12.50%）。在异烟肼（INH）单耐药菌株中，仅观察到两种突变：katG基因的S-315T1突变（50%）与inhA基因的C-15T突变（50%）。

结论与意义
改良MODS具有成本效益高、操作简便的优势，对检测人员的暴露风险极低，且未观察到样本间交叉污染的情况。因此，该方法可在低收入国家中用于结核病及其耐药性的早期检测。