Aim: To observe the induced resistance of Escherichia coli to a variety of fluoroquinolones in drug concentration of sub-M/C. Methods-.The experiments on induced resistance to ciprofloxacin.levofloxacin or gatifloxacin were performed, in thrity-two Escherichia coli sensitived to fluoroquinolones from clinic,respectively, by multiple-step method. The susceptibility of the induced strains resistant to fluoroquinolones was measured by determining the MIC using agar dilution method. Results:The strains highly resistant to fluoroquinolone were obtained from 22 tested strain of Escherichia coli,the MICs of these laboratory resistant strains were with 32 to 3 000 fold increase, respectively, when compared with parent strains. All six induced highly resistant strains examined carried two gyrA mutations affecting residues 83Ser→Leu,Asp87→ Asn and one parC mutation of 80Ser→Ile. No mutation was found in a susceptible isolate. Conclusion :Acquired resistance could be occurred when exposing to low level of some fluoroquinolones for long term.%目的:探讨大肠埃希菌在氟喹若酮类最低抑菌浓度(MIC)下耐药性的产生,以指导临床合理使用抗生素.方法:采用多步诱导法,对32株临床分离的氟喹诺酮类敏感大肠埃希菌分别进行环丙沙星、左氧氟沙星和加替沙星的诱导性耐药试验;用琼脂稀释法测定诱导前后敏感菌株的药物敏感性;用PCR方法测定耐药基因序列.结果:22株大肠埃希菌诱导出稳定的高耐氟喹诺酮菌株;与原株比较,耐药株的MIC分别增加了32～3 000倍;进行测序的6株诱导耐药菌株均发生gyrA的83Ser→Leu、87Asp→Ash和parc的80Ser→Ile突变,而测序的1株敏感菌株未发现基因突变.结论:在低浓度抗菌药物的长期压力下,可诱导大肠埃希菌产生对氟喹诺酮类的获得性耐药.
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