Ince Dilek, Zhang Xiamei, Silver L Christine, Hooper David C
Division of Infectious Diseases and Medical Services, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114-2696, USA.
Antimicrob Agents Chemother. 2003 Jan;47(1):274-82. doi: 10.1128/AAC.47.1.274-282.2003.
Gemifloxacin, a novel quinolone with potent activity against Staphylococcus aureus, was 8- to 16-fold more active against wild-type S. aureus than ciprofloxacin. The two- to fourfold increase in the MIC of gemifloxacin in genetically defined grlBA mutants and the twofold increase in a single gyrA mutant, supported by the low frequency of selection of resistant mutants at twice the MIC (7.4 x 10(-11) to 1.1 x 10(-10)), suggested similar targeting of the two enzymes by gemifloxacin. Dual mutations in both gyrase and topoisomerase IV caused a 64- to 128-fold increase in the MIC of gemifloxacin, similar to that seen with ciprofloxacin. Gemifloxacin also had similar activity in vitro against topoisomerase IV and gyrase purified from S. aureus (50% inhibitory concentrations of 0.25 and 0.31 micro g/ml, respectively). This activity was 10- to 20-fold higher than that of ciprofloxacin for topoisomerase IV and 33-fold higher than that for gyrase. In contrast to the in vitro findings, only topoisomerase IV mutants were selected in first-step mutants. Overexpression of the NorA efflux pump had a minimal effect on resistance to gemifloxacin, and a mutation in the promoter region of the gene for NorA was selected only in the sixth step of serial selection of mutants. Our data show that although gemifloxacin targets purified topoisomerase IV and gyrase similarly in vitro, topoisomerase IV is the preferred target in the bacteria. Selection of novel resistance mutations in grlA requires further expansion of quinolone-resistance-determining regions, and their study may provide increased insight into enzyme-quinolone interactions.
吉米沙星是一种对金黄色葡萄球菌具有强大活性的新型喹诺酮类药物，其对野生型金黄色葡萄球菌的活性比环丙沙星高8至16倍。在基因明确的grlBA突变体中，吉米沙星的最低抑菌浓度（MIC）增加了2至4倍，在单个gyrA突变体中增加了2倍，且在两倍MIC浓度下耐药突变体的选择频率较低（7.4×10⁻¹¹至1.1×10⁻¹⁰），这表明吉米沙星对这两种酶的作用靶点相似。gyrase和拓扑异构酶IV的双重突变导致吉米沙星的MIC增加了64至128倍，与环丙沙星的情况相似。吉米沙星对从金黄色葡萄球菌中纯化的拓扑异构酶IV和gyrase的体外活性也相似（50%抑制浓度分别为0.25和0.31μg/ml）。这种活性对拓扑异构酶IV比对环丙沙星高10至20倍，对gyrase高33倍。与体外研究结果相反，在第一步突变体中仅筛选出拓扑异构酶IV突变体。NorA外排泵的过表达对吉米沙星耐药性的影响极小，仅在突变体的连续筛选的第六步中才筛选到NorA基因启动子区域的突变。我们的数据表明，尽管吉米沙星在体外对纯化的拓扑异构酶IV和gyrase的作用靶点相似，但在细菌中拓扑异构酶IV是首选靶点。在grlA中选择新的耐药突变需要进一步扩大喹诺酮耐药决定区，对它们的研究可能会增加对酶 - 喹诺酮相互作用的了解。
