Mechanisms of Resistance to Folate Pathway Inhibitors in Burkholderia pseudomallei: Deviation from the Norm.
Mechanisms of Resistance to Folate Pathway Inhibitors in Burkholderia pseudomallei: Deviation from the Norm.
复制标题
DOI：
10.1128/mbio.01357-17
复制
发表时间：
2017-09-05
期刊：
影响因子：
6.4
通讯作者：
Schweizer HP
中科院分区：
文献类型：
--
作者：
Podnecky NL;Rhodes KA;Mima T;Drew HR;Chirakul S;Wuthiekanun V;Schupp JM;Sarovich DS;Currie BJ;Keim P;Schweizer HP
甲氧苄啶和磺胺甲恶唑组合，复方新诺明，在治疗类鼻疽伯克霍尔德菌感染中起着至关重要的作用。以前的研究表明，B。类鼻疽杆菌BpeEF-OprC外排泵在临床和环境分离株中赋予广泛的甲氧苄啶耐药性，但这并不伴随着对复方新诺明的显著耐药性。使用排除的选择剂菌株类鼻疽B. p82，我们现在表明，体外获得性甲氧苄啶与复方新诺明耐药性主要由bpeT突变引起的组成型BpeEF-OprC表达或bpeS突变引起的BpeEF-OprC过表达介导。bpeT突变影响BpeT LysR型激活蛋白的羧基末端效应物结合结构域。甲氧苄啶耐药性也可以由二氢叶酸还原酶（FolA）靶点突变介导，但除非BpeEF-OprC不存在，否则很少发生。BpeS是一种转录调节因子，与BpeT有62%的相同性。影响BpeS DNA结合或羧基末端效应物结合结构域的突变导致组成性BpeEF-OprC过表达，导致甲氧苄啶和磺胺甲恶唑外排，从而导致复方新诺明耐药。大多数实验室选择的复方新诺明耐药突变体通常也含有folM突变，编码蝶呤还原酶。对这些突变体的遗传分析表明，bpeS突变和folM突变均导致复方新诺明耐药，但folM的确切作用仍有待确定。影响bpeT、bpeS和folM的突变在复方新诺明耐药临床分离株中很常见，表明影响这些基因的突变具有临床意义。类鼻疽B菌对复方新诺明的耐药性是一个复杂的现象，这可以解释为什么这种细菌对这种药物的耐药性很罕见。类鼻疽伯克霍尔德氏菌引起类鼻疽，一种难以治疗的热带疾病。细菌对抗生素的耐药性限制了治疗选择。口服药物的缺乏进一步使治疗复杂化。选择的口服药物是复方新诺明，一种甲氧苄啶和磺胺甲恶唑的组合。这些抗生素靶向细菌四氢叶酸生物合成途径中的两种不同的酶，FolA（二氢叶酸还原酶）和FolP（二氢蝶酸合酶）。虽然由于双靶点抑制，复方新诺明耐药性最小化，但由于folA和folP突变导致的细菌耐药性确实发生。类鼻疽B杆菌对复方新诺明的耐药性很少见，尚未进行研究。该细菌中的复方新诺明耐药性采用了一种新的策略，该策略涉及决定耐药性概况的BpeEF-OprC外排泵表达的差异调节。贡献是影响folA的突变，但不是folP，和folM，叶酸途径相关的基因，其功能尚未得到很好的理解，以前没有涉及临床分离株中的叶酸抑制剂耐药性。
The trimethoprim and sulfamethoxazole combination, co-trimoxazole, plays a vital role in the treatment of Burkholderia pseudomallei infections. Previous studies demonstrated that the B. pseudomallei BpeEF-OprC efflux pump confers widespread trimethoprim resistance in clinical and environmental isolates, but this is not accompanied by significant resistance to co-trimoxazole. Using the excluded select-agent strain B. pseudomallei Bp82, we now show that in vitro acquired trimethoprim versus co-trimoxazole resistance is mainly mediated by constitutive BpeEF-OprC expression due to bpeT mutations or by BpeEF-OprC overexpression due to bpeS mutations. Mutations in bpeT affect the carboxy-terminal effector-binding domain of the BpeT LysR-type activator protein. Trimethoprim resistance can also be mediated by dihydrofolate reductase (FolA) target mutations, but this occurs rarely unless BpeEF-OprC is absent. BpeS is a transcriptional regulator that is 62% identical to BpeT. Mutations affecting the BpeS DNA-binding or carboxy-terminal effector-binding domains result in constitutive BpeEF-OprC overexpression, leading to trimethoprim and sulfamethoxazole efflux and thus to co-trimoxazole resistance. The majority of laboratory-selected co-trimoxazole-resistant mutants often also contain mutations in folM, encoding a pterin reductase. Genetic analyses of these mutants established that both bpeS mutations and folM mutations contribute to co-trimoxazole resistance, although the exact role of folM remains to be determined. Mutations affecting bpeT, bpeS, and folM are common in co-trimoxazole-resistant clinical isolates, indicating that mutations affecting these genes are clinically significant. Co-trimoxazole resistance in B. pseudomallei is a complex phenomenon, which may explain why resistance to this drug is rare in this bacterium. Burkholderia pseudomallei causes melioidosis, a tropical disease that is difficult to treat. The bacterium’s resistance to antibiotics limits therapeutic options. The paucity of orally available drugs further complicates therapy. The oral drug of choice is co-trimoxazole, a combination of trimethoprim and sulfamethoxazole. These antibiotics target two distinct enzymes, FolA (dihydrofolate reductase) and FolP (dihydropteroate synthase), in the bacterial tetrahydrofolate biosynthetic pathway. Although co-trimoxazole resistance is minimized due to two-target inhibition, bacterial resistance due to folA and folP mutations does occur. Co-trimoxazole resistance in B. pseudomallei is rare and has not yet been studied. Co-trimoxazole resistance in this bacterium employs a novel strategy involving differential regulation of BpeEF-OprC efflux pump expression that determines the drug resistance profile. Contributing are mutations affecting folA, but not folP, and folM, a folate pathway-associated gene whose function is not yet well understood and which has not been previously implicated in folate inhibitor resistance in clinical isolates.