embCAB sequence variation among ethambutol-resistant Mycobacterium tuberculosis isolates without embB306 mutation
embCAB sequence variation among ethambutol-resistant Mycobacterium tuberculosis isolates without embB306 mutation
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DOI：
10.1093/jac/dkq120
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发表时间：
2010-07-01
影响因子：
5.2
通讯作者：
Niemann, Stefan
中科院分区：
文献类型：
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作者：
Plinke, Claudia;Cox, Helen S.;Niemann, Stefan
目的：结核分枝杆菌对乙胺丁醇的耐药机制仍未得到充分的描述。尽管有越来越多的证据表明embB中密码子306的突变起着关键作用，但相当数量的表型乙胺丁醇耐药菌株不携带该密码子突变。这里，emcab操纵子的其他突变被认为参与了耐药性的发展。方法：对34株无embB306突变的表型乙胺丁醇耐药结核分枝杆菌和12株乙胺丁醇敏感结核分枝杆菌的embbcab操纵子进行分析。此外，106个对照菌株仅对特定突变的存在进行了调查。结果：总体而言，在乙胺丁醇耐药菌株中鉴定出15个不同密码子的18个非同义突变，而在乙胺丁醇敏感菌株中未发现。大多数发生在embB基因（10个不同的密码子），位于一个570bp的区域，也包含embB306。embC和embA的突变很少发现，大多数情况下与embB的多态性相结合。在乙胺丁醇敏感株和耐药株中分别发现1个同义突变（embA 228 bp）和2个非同义突变（embCVal981Leu和embCArg738Gln），并证实它们分别代表北京、哈勒姆和德里/CAS基因型菌株的系统发育标记。结论：除embB306突变外，embB406和embB497突变被确认为乙胺丁醇耐药临床分离株基因组变异的热点。在所有耐药菌株中，70.6%在embB的一个相对较短的区域携带突变，因此，这是一个有希望的目标，可用于快速检测乙胺丁醇耐药性的分子分析。
Objectives: Mechanisms of resistance to ethambutol in Mycobacterium tuberculosis remain inadequately described. Although there is mounting evidence that mutations of codon 306 in embB play a key role, a significant number of phenotypically ethambutol-resistant strains do not carry mutations in this codon. Here, other mutations in the embCAB operon are suggested to be involved in resistance development.Methods: The entire embCAB operon (similar to 10 kb) was analysed in 34 phenotypically ethambutol-resistant M. tuberculosis strains without mutations in embB306 and in 12 ethambutol-susceptible strains. Furthermore, 106 control strains were investigated for the presence of particular mutations only.Results: Overall, 18 non-synonymous mutations in 15 distinct codons of the embCAB operon were identified in ethambutol-resistant strains but not in ethambutol-susceptible isolates. The majority occurred in the embB gene (10 distinct codons), in a 570 bp region also encompassing embB306. Mutations in embC and embA were found rarely and in most cases in combination with polymorphisms in embB. One synonymous mutation (embA 228 bp) and two non-synonymous mutations (embCVal981Leu and embCArg738Gln) were found in ethambutol-susceptible strains as well as resistant strains and were confirmed to represent phylogenetic markers for strains of the Beijing, Haarlem and Delhi/CAS genotypes, respectively.Conclusions: Besides mutations in embB306, mutations in embB406 and embB497 were confirmed as hot spots for genomic variation in ethambutol-resistant clinical isolates. Of all resistant strains 70.6% carry a mutation in a relatively short region in embB, which therefore represents a promising target for inclusion in molecular assays for rapid detection of ethambutol resistance.