Department of International Cooperation, Japan Anti-Tuberculosis Association, 3-1-24 Matsuyama Kiyose-shi, Tokyo 204-8533, Japan; Department of Mycobacterium Reference and Research, Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, 3-1-24 Matsuyama Kiyose-shi, Tokyo 204-8533, Japan.
Department of Mycobacterium Reference and Research, Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, 3-1-24 Matsuyama Kiyose-shi, Tokyo 204-8533, Japan.
J Microbiol Methods. 2014 Jun;101:44-8. doi: 10.1016/j.mimet.2014.03.014. Epub 2014 Apr 6.
The aim of this study is to determine the appropriate cut-off value and turnaround time of the microscopic observation drug susceptibility assay (MODS) for isoniazid (INH), rifampicin (RMP), streptomycin (STR), and ethambutol (EMB).
A total of 39 Mycobacterium tuberculosis strains with confirmed drug susceptibility (reference strains) were tested with a range of drug concentrations to determine the optimal cut-off values for INH, RMP, STR, and EMB by MODS. Standard drug susceptibility testing (DST) results were evaluated relative to the Löwenstein-Jensen (L-J) proportion method. Following which, the performance of MODS was evaluated again using 36 sputum samples from patients with tuberculosis (TB) using the cut-off values determined in the aforementioned process.
With 39 reference strains, DST identified the following cut-off values: 0.8μg/ml INH (sensitivity, 96.0%; specificity, 92.9%), 2.0μg/ml RMP (sensitivity, 100%; specificity, 95.5%), 4.0μg/ml STR (sensitivity, 90.5%; specificity, 93.8%), and 4.0μg/ml EMB (sensitivity, 100%; specificity, 91.7%). When these cut-off values were used to analyze the 36 clinical isolates, the sensitivity and specificity of MODS were 100% and 93.1% for INH, 100% and 93.8% for RMP, 87.5% and 96.4% for STR, and 100% and 88.2% for EMB, respectively. The turnaround time for these clinical specimens was 9.0days by MODS (95% CI: 5.3-12.7), compared with 11.7days (95% CI: 9.5-13.9) for smear negative specimens.
Our study identified the optimal cut-off values of the four first-line drugs for MODS based on a wide concentration range. With the optimal cut-off values determined in this study, MODS showed high discriminatory efficiency for DST. This study also demonstrated that MODS is useful for rapid diagnosis of drug-resistant TB even for a smear negative specimen, despite the fact that it generally uses smear positive specimens as direct DST.
本研究旨在确定分枝杆菌微量药物敏感性检测（MODS）对异烟肼（INH）、利福平（RMP）、链霉素（STR）和乙胺丁醇（EMB）的适宜截止值和周转时间。
对 39 株经确认药物敏感性的结核分枝杆菌（参考株）进行一系列药物浓度检测，通过 MODS 确定 INH、RMP、STR 和 EMB 的最佳截止值。用 Löwenstein-Jensen（L-J）比例法对标准药物敏感性检测（DST）结果进行评估。然后，使用 36 例结核病（TB）患者的痰标本，根据上述过程确定的截止值，再次评估 MODS 的性能。
用 39 株参考株进行 DST 鉴定，得到以下截止值：0.8μg/ml INH（敏感性 96.0%，特异性 92.9%）、2.0μg/ml RMP（敏感性 100%，特异性 95.5%）、4.0μg/ml STR（敏感性 90.5%，特异性 93.8%）和 4.0μg/ml EMB（敏感性 100%，特异性 91.7%）。当使用这些截止值分析 36 例临床分离株时，MODS 对 INH 的敏感性和特异性分别为 100%和 93.1%，对 RMP 为 100%和 93.8%，对 STR 为 87.5%和 96.4%，对 EMB 为 100%和 88.2%。这些临床标本的周转时间为 9.0 天（95%CI：5.3-12.7），而阴性痰标本为 11.7 天（95%CI：9.5-13.9）。
本研究在较宽的浓度范围内确定了 MODS 四种一线药物的最佳截止值。根据本研究确定的最佳截止值，MODS 对 DST 具有较高的鉴别效率。本研究还表明，MODS 即使对阴性痰标本也可用于快速诊断耐药性结核，尽管它通常使用阳性痰标本进行直接 DST。
