National Reference Laboratory for Mycobacteria, Unité de recherché 12SP18, A Mami Pneumology Hospital, Ariana, Faculty of Mathematical, Physical and Natural Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia.
Emerging Bacterial Pathogens Unit, Division of Immunology, Transplantation and Infectious Diseases, Istituto di Ricovero e Cura a Carattere Scientifico San Raffaele Scientific Institute, Milan, Italy.
Int J Tuberc Lung Dis. 2018 Jun 1;22(6):661-666. doi: 10.5588/ijtld.17.0715.
Phenotypic tests used to detect pyrazinamide (PZA) resistance are slow and have a high rate of false resistance.
To evaluate the accuracy of pncA sequencing for the detection of PZA resistance in Mycobacterium tuberculosis strains isolated in Tunisia.
A total of 82 isolates, 41 resistant and 41 susceptible to PZA on BACTEC™ MGIT™ 960, were sequenced for pncA. Whole genome sequencing was performed for strains that were phenotypically resistant and had wild-type pncA in addition to MGIT retesting with a modified protocol.
Twenty-three strains resistant to PZA with negative pyrazinamidase (PZase) activity harboured a mutation in the promoter or coding region of pncA. However, 18 strains resistant to PZA did not present any mutation. Repeat MGIT 960 showed that 16 of 18 M. tuberculosis isolates were falsely resistant to PZA. Compared with MGIT, PZase activity assay and pncA sequencing both presented a sensitivity of 92.0% (95%CI 73.9-99.0) and a specificity of respectively 96.5% (positive predictive value [PPV] 92.0%, negative predictive value [NPV] 96.5%) and 100.0% (PPV 100.0%, NPV 96.6%).
The standard MGIT assay showed a high rate of false resistance to PZA, and the PZase activity assay is slow. pncA sequencing could therefore represent a rapid, accurate, alternative test to detect PZA resistance.
用于检测吡嗪酰胺（PZA）耐药性的表型检测方法缓慢，且耐药性假阳性率较高。
评估 pncA 测序检测突尼斯分离的结核分枝杆菌菌株中 PZA 耐药性的准确性。
总共对 82 株分离株进行 pncA 测序，其中 41 株对 BACTEC™ MGIT™ 960 中的 PZA 耐药，41 株对 PZA 敏感。对表型耐药且 pncA 为野生型的菌株进行全基因组测序，此外还对 MGIT 进行了改良方案的重新检测。
23 株对 PZA 耐药且吡嗪酰胺酶（PZase）活性阴性的菌株在 pncA 的启动子或编码区存在突变。然而，18 株对 PZA 耐药的菌株并未出现任何突变。重复 MGIT 960 显示，18 株结核分枝杆菌分离株中有 16 株对 PZA 存在假耐药。与 MGIT 相比，PZase 活性测定和 pncA 测序均表现出 92.0%（95%CI 73.9-99.0）的敏感性和分别为 96.5%（阳性预测值 [PPV] 92.0%，阴性预测值 [NPV] 96.5%）和 100.0%（PPV 100.0%，NPV 96.6%）的特异性。
标准 MGIT 检测法显示出对 PZA 耐药的高假阳性率，而 PZase 活性测定法较为缓慢。因此，pncA 测序可以作为一种快速、准确的替代检测方法来检测 PZA 耐药性。
