环丙沙星浓度对大肠埃希菌qnrA基因的影响

Effect of Ciprofloxacin concentration on Escherichia coli

[目的]研究携带qnrA基因的大肠埃希菌在环丙沙星压力下gyrA基因的突变情况及防耐药变异浓度(MPC)。[方法]采用质粒结合实验构建出携带qnrA基因且gyrA基因未发生突变的结合子。在不同浓度环丙沙星药物平皿上观察gyrA基因突变情况及对防耐药变异浓度的影响。[结果]结合子(菌株4E、5E)的突变选择指数(MPC/M IC)分别为24.0和35.0,平均突变率分别为0.6852和0.5500;阴性对照大肠埃希菌ATCC25922的突变选择指数为6.25,平均突变率为0.2078,与结合子比较差异有显著性意义(P<0.05)。[结论]携带qnrA基因的菌株在环丙沙星压力下,更容易发生gyrA基因突变,导致产生对环丙沙星的高水平耐药和高MPC。

[ Objective ] To study the mutation of ciprofloxacin selection pressure on the gyrA gene with qnrA gene positive strains and the MPC. [ Methods] Transconjugants were selected by plasmid conjugation tests, which with qnrA genes and gyrA genes had no mutation. The mutation of gyrA genes and MPC under ciprofloxacin concentration selection pressure was investigated. [ Results] The mutation selection exponent （MPC/MIC） of transconjugants （ strains 4E and 5E） were 24.0 and 35.0, and the average mutation rate were 0. 6852 and 0. 5500. The MPC/MIC of negative control Eseherichia coli ATCC 25922 was 6.25, and the average mutation rate was 0. 2078. The negative control, compared with the transconjugants had an increased significant deviation （ P 〈 0.05 ）. [ Conclusion ] The gyrA genes with qnrA genes positive strains are more apt to produce mutation under ciprofloxacin concentration selection pressure, and they play an important role in the high -level quinolone resistance and high MPC.