Lavender Caroline, Globan Maria, Sievers Aina, Billman-Jacobe Helen, Fyfe Janet
Department of Microbiology and Immunology, The University of Melbourne, Victoria, Australia.
Antimicrob Agents Chemother. 2005 Oct;49(10):4068-74. doi: 10.1128/AAC.49.10.4068-4074.2005.
Elucidation of the molecular basis of isoniazid (INH) resistance in Mycobacterium tuberculosis has led to the development of different genotypic approaches for the rapid detection of INH resistance in clinical isolates. Mutations in katG, in particular the S315T substitution, are responsible for INH resistance in a large proportion of tuberculosis cases. However, the frequency of the katG S315T substitution varies with population samples. In this study, 52 epidemiologically unrelated clinical INH-resistant M. tuberculosis isolates collected in Australia were screened for mutations at katG codon 315 and the fabG1-inhA regulatory region. Importantly, 52 INH-sensitive isolates, selected to reflect the geographic and genotypic diversity of the isolates, were also included for comparison. The katG S315T substitution and fabG1-inhA -15 C-to-T mutation were identified in 34 and 13 of the 52 INH-resistant isolates, respectively, and none of the INH-sensitive isolates. Three novel katG mutations, D117A, M257I, and G491C, were identified in three INH-resistant strains with a wild-type katG codon 315, fabG1-inhA regulatory region, and inhA structural gene. When analyzed for possible associations between resistance mechanisms, resistance phenotype, and genotypic groups, it was found that neither the katG S315T nor fabG1-inhA -15 C-to-T mutation clustered with any one genotypic group, but that the -15 C-to-T substitution was associated with isolates with intermediate INH resistance and isolates coresistant to ethionamide. In total, 90.4% of unrelated INH-resistant isolates could be identified by analysis of just two loci: katG315 and the fabG1-inhA regulatory region.
对结核分枝杆菌中异烟肼（INH）耐药性分子基础的阐明，促使人们开发出不同的基因分型方法，用于快速检测临床分离株中的INH耐药性。katG基因的突变，尤其是S315T替换，在很大比例的结核病病例中导致INH耐药。然而，katG S315T替换的频率因人群样本而异。在本研究中，对在澳大利亚收集的52株流行病学上无关联的临床INH耐药结核分枝杆菌分离株进行了katG密码子315和fabG1-inhA调控区突变的筛查。重要的是，还纳入了52株INH敏感分离株用于比较，这些分离株的选择反映了分离株的地理和基因分型多样性。在52株INH耐药分离株中，分别有34株和13株鉴定出katG S315T替换和fabG1-inhA -15 C→T突变，而所有INH敏感分离株均未检测到这些突变。在3株具有野生型katG密码子315、fabG1-inhA调控区和inhA结构基因的INH耐药菌株中，鉴定出3种新的katG突变，即D117A、M257I和G491C。在分析耐药机制、耐药表型和基因分型组之间的可能关联时发现，katG S315T突变和fabG1-inhA -15 C→T突变均未与任何一个基因分型组聚集，但-15 C→T替换与INH中度耐药分离株以及对乙硫异烟胺同时耐药的分离株相关。通过对仅两个位点：katG315和fabG1-inhA调控区的分析，总共可鉴定出90.4%的无关联INH耐药分离株。
