3种喹诺酮类药物对金黄色葡萄球菌及其耐药突变体的体外抗菌活性研究

Antibacterial Activity of Three Quinolones Against Staphylococcus aureus in Vitro

目的比较左氧氟沙星、莫西沙星和奈诺沙星对金黄色葡萄球菌的体外抗菌活性,初步探索金黄色葡萄球菌gyrA和parC基因突变对3种抗菌药物耐药性的影响及3种药物对金黄色葡萄球菌gyrA和parC基因的优先作用顺序。方法利用琼脂平板稀释法测定左氧氟沙星、莫西沙星和奈诺沙星分别对50株金黄色葡萄球菌的最低抑菌浓度(minimal inhibitory concentration,MIC);测定4株已知特定基因位点细菌(其中RN450为实验室菌株,已知基因序列,无任何位点突变)的MIC和防耐药突变浓度(mutant prevention concentration,MPC),在已知MIC和MPC基础上考察4株细菌的恢复生长细菌情况,对恢复生长细菌进行菌落计数并描记细菌恢复生长曲线。结果左氧氟沙星对50株金黄色葡萄球菌的MIC90(可抑制90%细菌生长的药物浓度)(16μg·m L^(-1))分别是莫西沙星(2μg·m L^(-1))和奈诺沙星(0.5μg·m L^(-1))的8倍和32倍。从细菌恢复曲线上来看,在相同药物浓度时,对于不同药物来说,奈诺沙星的恢复生长细菌比例最小,而左氧氟沙星的恢复生长细菌比例最大;对于不同位点突变的细菌来说,RN450的恢复生长比例最小,而RN450A3的恢复生长比例最大。结论 3种药物对金黄色葡萄球菌的体外抗菌活性强弱顺序为:奈诺沙星>莫西沙星>左氧氟沙星;相较于左氧氟沙星和莫西沙星,奈诺沙星可在较低浓度时抑制细菌生长,且对不同基因位点突变细菌均有强大抑制作用。左氧氟沙星可能优先作用于金黄色葡萄球菌的拓扑异构酶Ⅳ的parC基因,而莫西沙星和奈诺沙星则可能几乎同时作用于金黄色葡萄球菌DNA旋转酶的gyrA基因和拓扑异构酶Ⅳ的parC基因。

OBJECTIVE To evaluate the antibacterial activity of levofloxacin, moxifloxacin and nemonoxacin against Staphylo- coccus aureus in vitro. To assesse the impact of gyrA and parC genes mutant on resistance for quinolones and the sequences of gyrA and parC genes for three quinolones. METHODS The MICs of 50 S. aureus were detected by agar dilution method. The MIC and MPC against four S. aureus which were special gene mutations were detected by agar dilution method. Based on these results, bacterial re- covery growth curve of levofloxacin, moxifloxacin and nemonoxacin were traced. RESULTS Nemonoxacin demonstrated activities 8- to 32- fold more potent（ MICs at which 90% of isolates were inhibited [ MIC90s] , 0. 5 μg · mL -1 ） than those of moxifloxacin（ MIC90, 2 μg · mL - 1 ） and levofloxacin （ MIC90, 16 μg · mL-1 ） against 50 S. aureus. In condition of the same drug concentrations, the bacte- rial recovery growth ratios of nemonoxacin was the lowest, while levofloxacin＇s was the highest. RN450A3 recovery growth ratio was highest compared with other mutant bacterial strains, while RN450 recovery growth ratio was lowest. CONCLUSION The antibacteri- al activities of nemonoxacin, moxifloxacin and levofloxacin against S. aureus in vitro are ： nemonoxacin 〉 moxifloxacin 〉 levofloxacin. Compared with levofloxacin and moxifloxacin, nemonoxacin inhibits bacteria in a lower concentration, and nemonoxacin is utterly effi- cacious with different genes mutant strains. The target preference of levofloxacin may be the parC gene of topoisomerase IV, while moxi- floxacin and nenomoxacin can almost act on the gyrA and parC gene at the same time.