Department of Urology, Shin-Kokura Hospital, Federation of National Public Service and Affiliated Personnel Mutual Aid Association, Kitakyushu, 803-0816, Japan; Department of Urology, University of Occupational and Environmental Health, Kitakyushu, 807-8555, Japan.
Daiichi Sankyo RD Novare, Co. Ltd, Tokyo, 134-8630, Japan.
J Infect Chemother. 2022 Mar;28(3):377-383. doi: 10.1016/j.jiac.2021.11.011. Epub 2021 Nov 24.
The mechanisms of fluoroquinolone-resistance of Mycoplasma genitalium were analysed by a new method.
M. genitalium strains from urinary sediments of patients with urethritis were isolated and examined antimicrobial susceptibilities and the mutations in ParC, GyrA and 23S rRNA. Docking models between gyrase and topoisomerase IV with sitafloxacin showed that two binding modes in which the amine moiety at the C-7 position rotated could be constructed.
Among 18 strains, 13 strains had mutations with amino-acid changes at Serine 83 in ParC. The MICs of moxifloxacin or sitafloxacin for three strains with only S83I in ParC were 2, 1 and 8 mg/L (moxifloxacin) or 0.13, 0.13 and 1 mg/L (sitafloxacin), respectively. In contrast, the MICs of moxifloxacin or sitafloxacin for 3 strain with S83N in ParC were 0.25, 0.13 and 0.25 mg/L (moxifloxacin) or 0.06, 0.03, and 0,03 mg/L (sitafloxacin), respectively, not significantly different from wild-type isolates. The docking model of sitafloxacin and topoisomerase IV showed that the oxygen atom at the gamma position of Serine 83 of ParC interacted with the sitafloxacin carboxylate moiety. When the S83I substitution occurs, the isoleucine side chain is lipophilic and the residue hydropathy changes from hydrophilicity to hydrophobicity and important H-bond interactions between serine and the carboxylate moiety are lost. When the serine 83 to asparagine substitution (S83N) occurred, the asparagine side chain is hydrophilic and the residue hydropathy does not change.
The docking model suggests that Ser83 replacements causes attenuation or loss of activity of fluoroquinolones such as sitafloxacin.
本研究采用新方法分析解脲支原体对氟喹诺酮类药物耐药的机制。
从尿道炎患者尿沉渣中分离解脲支原体菌株，检测其抗菌药物敏感性及 ParC、GyrA 和 23S rRNA 突变情况。利用对接模型分析吉西沙星与拓扑异构酶 IV 与 gyrase 的结合方式，发现 C-7 位的氨基可以发生两种旋转构象。
在 18 株菌中，有 13 株菌 ParC 第 83 位丝氨酸发生氨基酸改变。3 株菌仅存在 ParC 第 83 位丝氨酸突变为 Ile（S83I）时，对莫西沙星或西他沙星的 MIC 值分别为 2、1 和 8mg/L（莫西沙星）或 0.13、0.13 和 1mg/L（西他沙星）；而 3 株菌存在 ParC 第 83 位丝氨酸突变为 Asn（S83N）时，对莫西沙星或西他沙星的 MIC 值分别为 0.25、0.13 和 0.25mg/L（莫西沙星）或 0.06、0.03 和 0mg/L（西他沙星），与野生型菌株无显著差异。西他沙星与拓扑异构酶 IV 的对接模型显示，ParC 第 83 位丝氨酸的γ位氧原子与西他沙星的羧基部分相互作用。当 S83I 取代发生时，异亮氨酸侧链为疏水性，残基疏水性从亲水性变为疏水性，丝氨酸与羧基部分的重要氢键相互作用丢失。当丝氨酸 83 突变为天冬酰胺（S83N）时，天冬酰胺侧链为亲水性，残基疏水性不变。
对接模型提示，Ser83 取代导致西他沙星等氟喹诺酮类药物活性降低或丧失。
