Heaton V J, Ambler J E, Fisher L M
Molecular Genetics Group, Department of Biochemistry, St. George's Hospital Medical School, University of London, London SW17 0RE, United Kingdom.
Antimicrob Agents Chemother. 2000 Nov;44(11):3112-7. doi: 10.1128/AAC.44.11.3112-3117.2000.
We investigated the roles of DNA gyrase and topoisomerase IV in determining the susceptibility of Streptococcus pneumoniae to gemifloxacin, a novel fluoroquinolone which is under development as an antipneumococcal drug. Gemifloxacin displayed potent activity against S. pneumoniae 7785 (MIC, 0.06 microgram/ml) compared with ciprofloxacin (MIC, 1 to 2 microgram/ml). Complementary genetic and biochemical approaches revealed the following. (i) The gemifloxacin MICs for isogenic 7785 mutants bearing either parC or gyrA quinolone resistance mutations were marginally higher than wild type at 0.12 to 0.25 microgram/ml, whereas the presence of both mutations increased the MIC to 0.5 to 1 microgram/ml. These data suggest that both gyrase and topoisomerase IV contribute significantly as gemifloxacin targets in vivo. (ii) Gemifloxacin selected first-step gyrA mutants of S. pneumoniae 7785 (gemifloxacin MICs, 0.25 microgram/ml) encoding Ser-81 to Phe or Tyr, or Glu-85 to Lys mutations. These mutants were cross resistant to sparfloxacin (which targets gyrase) but not to ciprofloxacin (which targets topoisomerase IV). Second-step mutants (gemifloxacin MICs, 1 microgram/ml) exhibited an alteration in parC resulting in changes of ParC hot spot Ser-79 to Phe or Tyr. Thus, gyrase appears to be the preferential in vivo target. (iii) Gemifloxacin was at least 10- to 20-fold more effective than ciprofloxacin in stabilizing a cleavable complex (the cytotoxic lesion) with either S. pneumoniae gyrase or topoisomerase IV enzyme in vitro. These data suggest that gemifloxacin is an enhanced affinity fluoroquinolone that acts against gyrase and topoisomerase IV in S. pneumoniae, with gyrase the preferred in vivo target. The marked potency of gemifloxacin against wild type and quinolone-resistant mutants may accrue from greater stabilization of cleavable complexes with the target enzymes.
我们研究了DNA旋转酶和拓扑异构酶IV在决定肺炎链球菌对吉米沙星敏感性方面的作用。吉米沙星是一种正在开发用作抗肺炎球菌药物的新型氟喹诺酮类药物。与环丙沙星（MIC，1至2微克/毫升）相比，吉米沙星对肺炎链球菌7785显示出强大的活性（MIC，0.06微克/毫升）。互补的遗传学和生物化学方法揭示了以下几点。（i）携带parC或gyrA喹诺酮耐药突变的同基因7785突变体的吉米沙星MIC在0.12至0.25微克/毫升时略高于野生型，而两种突变同时存在则使MIC增加到0.5至1微克/毫升。这些数据表明，旋转酶和拓扑异构酶IV在体内作为吉米沙星的靶点都有显著作用。（ii）吉米沙星筛选出了肺炎链球菌7785的第一步gyrA突变体（吉米沙星MIC，0.25微克/毫升），其编码Ser-81突变为Phe或Tyr，或Glu-85突变为Lys。这些突变体对司帕沙星（靶向旋转酶）交叉耐药，但对环丙沙星（靶向拓扑异构酶IV）不耐药。第二步突变体（吉米沙星MIC，1微克/毫升）表现出parC的改变，导致ParC热点Ser-79突变为Phe或Tyr。因此，旋转酶似乎是体内的优先靶点。（iii）在体外，吉米沙星在稳定与肺炎链球菌旋转酶或拓扑异构酶IV酶形成的可裂解复合物（细胞毒性损伤）方面比环丙沙星至少有效10至20倍。这些数据表明，吉米沙星是一种亲和力增强的氟喹诺酮类药物，作用于肺炎链球菌中的旋转酶和拓扑异构酶IV，旋转酶是体内的首选靶点。吉米沙星对野生型和喹诺酮耐药突变体的显著效力可能源于与靶酶形成的可裂解复合物的更大稳定性。
