中文摘要：

目的研究不同药物浓度、不同化学结构的氟喹诺酮类药物对突变选择窗（MSW）内筛选的大肠埃希菌耐药突变体的靶位基因的影响。方法应用5种氟喹诺酮类药物在突变选择窗内接种约1×10^10菌量的ATCC25922筛选耐药突变体；用琼脂平板二倍稀释法测定ATCC25922和耐药突变体的MIC；用PCR及DNA测序方法确定ATCC25922和耐药突变体耐药决定簇（QRDRs）的gyrA、parC的突变位点和相应的氨基酸变化。结果在ATCC25922的MSW中，筛选53株耐药突变体，所有突变体均为gyrA位点突变，无parC位点突变。其中有79％（42株）为Set-83→Leu位点突变，19％（10株）为Asp-87→Asn，2％（1株）为Gly81→cys位点突变；83位和87位为大肠埃希菌的常见突变位点。氟喹诺酮对Set-83→h突变体的MIC。较Gly81→Cys突变体的MIC90高2～8倍，较Asp-87→Asn突变体的MIC90高1～2倍；Ser-83→Leu是所有的突变位点中对耐药影响最重要的位点。结论氟喹诺酮对大肠埃希菌的主要靶位是GyrA；83位和87位突变为大肠埃希菌最常见突变位点。

英文摘要：

Objective To investigate the concentration,structure of fluoroquinolones on the target gene mutation of Escherichia colii mutants selected in the mutant selection window （MSW）. Methods The target genes, gyrA and parC of Escherichia colii mutants selected in the MSW were obtained by PCR method and sequenced by DNA sequencing. The agar dilution method was carried out to determine minimal inhibition concentration （MIC） of Escherichia coli mutants. Results Among 53 mutants selected by five fluoroquinolones, 79% were Set - 83 - Leu mutation detected in the quinolone resistant - determining region of the gyrA gene, 19% were Asp- 87Asn mutation, 2% was a Gly81 -Cys mutation, and no parC mutation was detectable. MIC90 of mutation at position 83 was 2 ～ 8 fold larger than that of mutation at position 81 and 1～2 fold larger than that of mutation at position 87. Mutation at position 83 was the most important factor to influence the sensitivity of Escherichia coli. Conclusion DNA gyrase is the primary target of fluoroquinolone against E. coli, mutation at position 83 and 87 is the most frequent.