ethA, inhA, and katG loci of ethionamide-resistant clinical Mycobacterium tuberculosis isolates
ethA, inhA, and katG loci of ethionamide-resistant clinical Mycobacterium tuberculosis isolates
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DOI：
10.1128/aac.47.12.3799-3805.2003
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发表时间：
2003-12-01
影响因子：
4.9
通讯作者：
Cooksey, RC
中科院分区：
文献类型：
--
作者：
Morlock, GP;Metchock, B;Cooksey, RC
异烟酰胺（ETH）是抗结核药物异烟肼（INH）的结构类似物。这两种药物都靶向InhA，一种参与分枝菌酸生物合成的酶。INH需要过氧化氢酶-过氧化物酶（KatG）激活，并且KatG中的突变是主要的INH抗性机制。最近，已经鉴定了能够激活ETH的酶（EthA）。我们对41株耐ETH结核分枝杆菌分离株的ethA结构基因进行了全序列测定。我们还对inhA的两个区域和katG的全部或部分进行了测序。测定ETH和INH的MIC，以将鉴定的突变与耐药表型相关联。发现15个分离株具有ethA突变，所有这些ETH MIC均大于或等于50 μ g/ml。ethA突变都是不同的，以前没有报道过，并且分布在整个基因中。在8个分离株中，inhA结构基因发生错义突变。七个InhA突变体的ETH MIC大于或等于100 μ g/ml，并且这些分离物也对大于或等于8 μ g/ml的INH具有抗性。在14个分离株中仅发现了inhA启动子中的单个点突变。15个分离株发生katG突变，除1个外，所有分离株的INH MIC均大于或等于32 μ g/ml。正如预期的那样，我们发现katG突变与ETH耐药水平之间没有关联。ethA和inhA结构基因内的突变与相对高水平的ETH抗性相关。大约76%的耐大于或等于50 μ g/ml ETH的分离株有这样的突变。
Ethionamide (ETH) is a structural analog of the antituberculosis drug isoniazid (INH). Both of these drugs target InhA, an enzyme involved in mycolic acid biosynthesis. INH requires catalase-peroxidase (KatG) activation, and mutations in katG are a major INH resistance mechanism. Recently an enzyme (EthA) capable of activating ETH has been identified. We sequenced the entire ethA structural gene of 41 ETH-resistant Mycobacterium tuberculosis isolates. We also sequenced two regions of inhA and all or part of katG. The MICs of ETH and INH were determined in order to associate the mutations identified with a resistance phenotype. Fifteen isolates were found to possess ethA mutations, for all of which the ETH MICs were greater than or equal to50 mug/ml. The ethA mutations were all different, previously unreported, and distributed throughout the gene. In eight of the isolates, a missense mutation in the inhA structural gene occurred. The ETH MICs for seven of the InhA mutants were greater than or equal to100 mug/ml, and these isolates were also resistant to greater than or equal to8 mug of INH per ml. Only a single point mutation in the inhA promoter was identified in 14 isolates. A katG mutation occurred in 15 isolates, for which the INH MICs for all but 1 were greater than or equal to32 mug/ml. As expected, we found no association between katG mutation and the level of ETH resistance. Mutations within the ethA and inhA structural genes were associated with relatively high levels of ETH resistance. Approximately 76% of isolates resistant to greater than or equal to50 mug of ETH per ml had such mutations.