Susceptibility of Mycobacterium tuberculosis clinical isolates to moxifloxacin

背景：莫西沙星是一种新一代喹诺酮类药物，目前正在临床试验中作为一线抗结核药物进行评估。人类和动物数据表明，各种喹诺酮类药物之间存在交叉耐药，结核分枝杆菌（MTB）分离株的喹诺酮类耐药可影响治疗效果。目前还没有发表的关于一般人群中结核分枝杆菌临床分离株对莫西沙星或其他喹诺酮类药物耐药流行率的系统分析。此外，数据表明gyrA基因QRDR区域的突变仅占MTB分离株喹诺酮类药物耐药的42-85%，这表明QRDR外或其他基因的突变在MTB的喹诺酮类药物耐药中发挥了作用。具体目的：1)分析休斯敦、哈里斯县MTB临床分离株中莫西沙星、左氧氟沙星和氧氟沙星敏感性降低的结核分枝杆菌的流行情况。2)鉴定gyrA、gyrB和Rv2686c- Rv2687c-Rv2688c基因突变与所研究的喹诺酮类药物敏感性降低相关。方法：作为休斯敦市结核病控制工作的一部分，从哈里斯县休斯敦收集的约95%的结核分枝杆菌临床分离株被送往德克萨斯州卫生服务部。我们将采用琼脂比例间接药敏法，对所有结核分枝杆菌临床分离株进行为期24个月的异烟肼、利福平、乙胺丁醇、氧氟沙星、左氧氟沙星和莫西沙星耐药性的前瞻性测试。我们将从喹诺酮类药物敏感性降低的MTB分离株和匹配数量的喹诺酮类药物敏感性分离株中提取DNA，比较gyrA、gyrB和Rv2686c-Rv2687c-Rv2688c基因的序列；假定的或已证实的与喹诺酮类药物易感性有关的基因。结果/数据：研究结果将作为MTB耐莫西沙星患病率及其与一线抗结核药物和其他喹诺酮类药物耐药相关性的数据提出。将确定结核分枝杆菌中与喹诺酮类药物耐药相关的突变。这些数据将首次全面分析结核分枝杆菌分离株中喹诺酮类药物耐药的流行情况及其在一般人群中的遗传机制。2005年10月，结核病联盟（全球结核病药物开发联盟）和拜耳制药公司宣布了在临床试验中研究莫西沙星的计划，旨在缩短结核病治疗方案的长度，此前数十年的结核病药物开发极其缓慢。结核病患者对莫西沙星的耐药性可能会降低将其纳入结核病药物治疗方案的有效性，而且医学文献缺乏关于结核分枝杆菌（MTB）对莫西沙星的耐药性有多普遍的系统数据。我们拟系统研究从Harris县Houston收集的24个月的MTB患者中莫西沙星耐药情况，为设计更好的治疗方案提供数据依据，并为今后MTB中喹诺酮类药物耐药的监测和研究提供依据。

DESCRIPTION (provided by applicant): Background: Moxifloxacin, a later-generation quinolone, is currently undergoing evaluation in clinical trials for use as first-line antituberculous agent. Human and animal data suggest that there is cross resistance among various quinolones and that quinolone-resistance in Mycobacterium tuberculosis (MTB) isolates can affect the efficacy of the treatment. There are no published systematic analyses of the prevalence of resistance to moxifloxacin or other quinolones in MTB clinical isolates in the general population. Moreover, data suggest that mutations in the QRDR region of the gyrA gene account for only 42-85% of quinolone drug resistance in MTB isolates, suggesting that mutations outside the QRDR or in other genes play a role in quinolone resistance in MTB. Specific Aims: 1) To analyze the prevalence of MTB strains with reduced susceptibility to moxifloxacin, levofloxacin and ofloxacin in MTB clinical isolates from Houston, Harris County over 24 months and 2) To identify mutations in the gyrA, gyrB and Rv2686c- Rv2687c-Rv2688c genes that are associated with reduced susceptibility to the studied quinolones. Methods: As part of the tuberculosis control efforts in the city, >95% of MTB clinical isolates from Houston, Harris County are sent to the Texas State Department of Health Services. We will prospectively test all MTB clinical isolates for resistance to isoniazid, rifampin, ethambutol, ofloxacin, levofloxacin and moxifloxacin over a 24-month period, using the agar proportion indirect susceptibility method. We will extract the DNA from MTB isolates with reduced susceptibility to quinolones and a matched number of quinolone susceptible isolates to compare the sequences of the gyrA, gyrB and Rv2686c-Rv2687c-Rv2688c genes; genes of putative or demonstrated role in susceptibility to quinolones. Results/data: The study results will be presented as data on the prevalence of MTB moxifloxacin resistance and its correlation with resistance to first-line anti-TB drugs and other quinolones. Mutations associated with quinolone resistance in MTB will be identified. The data will represent the first comprehensive analysis of the prevalence of quinolone drug resistance in MTB isolates and its genetic mechanisms in the general population. In October 2005, TB Alliance (Global Alliance for tuberculosis (TB) drug development) and Bayer Pharmaceuticals announced plans to study moxifloxacin in clinical trials aiming at shortening the length of TB treatment regimens, after decades of exceedingly slow TB drug development. Resistance to moxifloxacin in TB can potentially reduce the effectiveness of its inclusion in TB drug regimens, and the medical literature lacks systemic data on how prevalent moxifloxacin resistance in Mycobacterium tuberculosis (MTB) is. We propose to systematically study the prevalence of moxifloxacin drug resistance in MTB strains collected from patients in Houston, Harris County over a period of 24 months, thus providing data that can be used as a too to help design better treatment regimens and provide the basis for future monitoring and research on the topic of quinolone drug resistance in MTB.