Jagielski Tomasz, Grzeszczuk Magdalena, Kamiński Michał, Roeske Katarzyna, Napiórkowska Agnieszka, Stachowiak Radosław, Augustynowicz-Kopeć Ewa, Zwolska Zofia, Bielecki Jacek
Department of Applied Microbiology, Institute of Microbiology, Faculty of Biology, University of Warsaw.
Pneumonol Alergol Pol. 2013;81(4):298-307.
A major role in the development of resistance of Mycobacterium tuberculosis to isoniazid (INH) is attributed to mutations in the katG gene coding for the catalase/peroxidase, an enzyme required for obtaining a pharmacologically active form of the drug. Analysis of mutations in the katG gene in M. tuberculosis strains may contribute to the development of reliable and rapid tests for detection of INH resistance. The aim of the study was to identify and characterize mutations in the katG gene in multidrug-resistant M. tuberculosis clinical isolates.
The study included 46 strains of M. tuberculosis, recovered from MDR-TB patients in Poland in 2004. Mutations in the katG gene were detected by comparing DNA sequences with the corresponding sequence of a wild-type reference laboratory strain (M. tuberculosis H37Rv). The obtained results were interpreted in the context of MIC values of INH and catalase activity of the strains tested.
A total of 43 (93%) strains contained mutations in the katG gene. The most frequently observed were mutations at codon 315, found in 34 (74%) strains. Mutations at other codons were rare: 4 strains contained mutations at codon 463, 2 at codon 131 and another 2 at codon 234. Mutations at codons 68, 91, 101, 126, 128 and 194 were found in single strains only. Two strains, for which no mutations at codon 315 of the katG gene were identified, had a unique translation termination mutation, which would invariably result in polypeptide truncation leading to the generation of dysfunctional catalase polypeptides. Both these strains presented the highest MIC values for INH (80 and 100 μg/mL) and showed a complete loss of catalase activity. For the remaining 41 strains with katG mutations, the MICs of INH were within the range 0.2-10 μg/mL. Thirty-six (88%) of those strains retained their catalase activity.
Mutations at codon 315 within the katG gene, depending on their type might be useful for the prediction of INH resistance. Whereas the missense mutations do not affect the catalase activity or the level of INH resistance, the nonsense mutations result in high-level resistance to INH and a total loss of catalase activity.
结核分枝杆菌对异烟肼（INH）耐药性的产生主要归因于编码过氧化氢酶/过氧化物酶的katG基因突变，该酶是获得药物药理活性形式所必需的。分析结核分枝杆菌菌株中katG基因的突变可能有助于开发可靠、快速的INH耐药性检测方法。本研究的目的是鉴定和表征耐多药结核分枝杆菌临床分离株中katG基因的突变。
本研究包括2004年从波兰耐多药结核病患者中分离出的46株结核分枝杆菌。通过将DNA序列与野生型参考实验室菌株（结核分枝杆菌H37Rv）的相应序列进行比较，检测katG基因的突变。根据所测菌株的INH MIC值和过氧化氢酶活性对所得结果进行解释。
共有43株（93%）菌株的katG基因发生突变。最常见的是密码子315处的突变，在34株（74%）菌株中发现。其他密码子的突变很少见：4株在密码子463处发生突变，2株在密码子131处，另外2株在密码子234处。仅在单株中发现密码子68、91、101、126、128和194处的突变。有2株未在katG基因密码子315处发现突变，它们有一个独特的翻译终止突变，这必然会导致多肽截断，从而产生功能失调的过氧化氢酶多肽。这两株菌株对INH的MIC值最高（80和100μg/mL），且过氧化氢酶活性完全丧失。对于其余41株有katG基因突变的菌株，INH的MIC值在0.2 - 10μg/mL范围内。其中36株（88%）保留了过氧化氢酶活性。
katG基因密码子315处的突变，根据其类型可能有助于预测INH耐药性。错义突变不影响过氧化氢酶活性或INH耐药水平，而无义突变导致对INH的高水平耐药和过氧化氢酶活性完全丧失。
