Functional Consequence of Macrolide Resistance Mutations in T. pallidum

描述（由申请人提供）：多年来，一直在寻求单剂量口服治疗梅毒。过去50年来用于治疗梅毒的苄星青霉素G有许多缺点，包括注射部位疼痛，过敏反应的可能性，以及这种形式的青霉素无法在中枢神经系统（梅毒螺旋体传播的常见部位）中达到杀螺旋体水平。已发表的使用兔梅毒模型的研究证明了阿奇霉素（一种与大环内酯类相关的口服氮杂内酯类抗生素）治疗由T.苍白球在几项人体研究中，1或2克剂量的阿奇霉素对治疗早期梅毒有效。然而，最近的出版物记录了循环T的23 S rRNA基因中的高频率突变A2058 G。苍白球菌株在其他细菌中，这种突变与大环内酯类耐药性有关。街14株T.梅毒包含A2058 G突变，并且在兔梅毒模型中，对大环内酯类和相关药物（包括阿奇霉素）具有抗性。同样，阿奇霉素治疗失败已被记录在患者感染T。含有相同突变的苍白球细菌。尽管如此，最近的一份出版物质疑这些23 S rDNA突变的临床相关性;在与疾病控制和预防中心制定新的梅毒治疗指南有关的讨论中也表达了类似的观点。 与其继续猜测，还不如进行实验，直接确定这些和其他突变是否影响阿奇霉素治疗的临床反应。尽管人们可能会争辩说，存在（或不存在）足够的平衡来证明阿奇霉素治疗感染有机体携带23 S rDNA突变的梅毒患者的试验是合理的，但不太可能在可以告知我们当前临床实践的时间范围内进行。建立完善的梅毒兔模型是解决这个问题的理想方法。本研究的主要目的是：1）确定T. 23 SrRNA基因A2058 G和A2059 G点突变的发生率; 2）对这些样本的一个子集中的全部23 s rRNA基因（两种等位基因）进行测序，以鉴定可能与大环内酯类耐药相关的其他突变;和3）在已建立的梅毒兔模型中测试所鉴定的突变与阿奇霉素治疗临床失败的相关性。为了有效地治疗梅毒患者，临床医生迫切需要知道T。苍白球23 S rDNA突变增加阿奇霉素治疗失败的风险我们的工作结果将提供一个证据基础，在此基础上可以提出合理的治疗建议。 公共卫生相关性：拟议的研究将1）确定引起梅毒的细菌突变是否影响阿奇霉素治疗的反应，2）确定含有这些突变的细菌在几个地理区域的梅毒患者中的存在频率。如果发现这些突变是常见的，并显示会导致治疗失败，医生将被建议不要使用阿奇霉素治疗梅毒患者。

DESCRIPTION (provided by applicant): For many years, a single-dose oral treatment for syphilis has been sought. Benzathine penicillin G, used to treat syphilis for the past 50 years, has many disadvantages, including pain at injection sites, the possibility of an allergic reaction, and the inability of this form of penicillin to achieve treponemacidal levels in the central nervous system (a common site for Treponema pallidum dissemination). Published studies using the rabbit syphilis model demonstrated the effectiveness of azithromycin, an oral azalide antibiotic related to macrolides, for treating syphilis caused by the Nichols strain of T. pallidum. In several human studies, a single 1 or 2 gram dose of azithromycin was effective for treatment of early syphilis. However, recent publications document high frequencies of mutation A2058G in the 23S rRNA genes of circulating T. pallidum strains. In other bacteria, this mutation is associated with macrolide resistance. The Street 14 strain of T. pallidum contains the A2058G mutation, and, in the rabbit syphilis model, is resistant to macrolide and related drugs, including azithromycin. Similarly, azithromycin treatment failure has been documented in patients infected with T. pallidum bacteria that contain the same mutation. Nonetheless, a recent publication has questioned the clinical relevance of these 23S rDNA mutations; similar views have been voiced in discussions related to the development of the new syphilis treatment guidelines by the Centers for Disease Control and Prevention. Rather than continuing to speculate, it is essential to conduct the experiments that will directly determine whether these and other mutations impact the clinical response to azithromycin therapy. Although one could argue that sufficient equipoise exists (or does not exist) to justify a trial of azithromycin for treatment of patients with syphilis whose infecting organism harbors a 23S rDNA mutation, it is unlikely to be conducted in a timeframe that can inform our current clinical practice. The well-established rabbit model of syphilis is ideal for addressing the issue. The goals of the proposed project are 1) to determine the prevalence of A2058G and A2059G point mutations in the 23s rRNA genes of T. pallidum in samples collected from patients in widely disparate geographic regions; 2) to sequence the full 23s rRNA genes (both alleles) in a subset of these samples to identify other mutations that might be associated with macrolide resistance; and 3) to test the correlation of the identified mutations with clinical failure of azithromycin treatment in the well-established rabbit model of syphilis. To effectively treat our patients with syphilis, clinicians urgently need to know whether T. pallidum 23S rDNA mutations confer risk for azithromycin treatment failure. The results of our work will provide an evidence base on which sound treatment recommendations can be made. PUBLIC HEALTH RELEVANCE: The proposed studies will 1) determine whether mutations in the bacterium that causes syphilis affect response to treatment with azithromycin and 2) determine how frequently bacteria containing these mutations are present in syphilis patients from several geographical regions. If these mutations are found to be common and are shown to cause treatment failure, physicians will be advised not to use azithromycin for treating patients with syphilis.