大肠埃希菌中氟喹诺酮耐药机制功能分析

Contributions of different quinolone resistance mechanisms in Escherichia coli

目的分析拓扑异构酶的突变和外排泵系统在大肠埃希菌（Escherichla coli）氟喹诺酮类药物耐药机制中的作用。方法本研究通过基因重组技术对大肠埃希菌中拓扑异构酶不同点突变的功能进行了准确测定，同时也对大肠埃希菌中不同外排泵及膜蛋白的功能进行了分析。结果在不同的菌株中，acrAB或tolC的切除所引起细菌耐药性的变化不同。对拓扑异构酶点突变的功能分析显示，gyrA中的点突变（S83和D87）在喹诺酮耐药机制中起主要作用，没有gyrA上的点突变，parC上的点突变（S80和A108）对细菌的耐药性不产生影响，但单独gyrA上的点突变（S83和D87）也仅导致敏感菌株对萘啶酸耐药，而对其他氟喹诺酮类药物仍表现为敏感。当对喹诺酮敏感的大肠埃希菌K-12同时具备gyrA（S83L和D87N）和parC（S80I和A108V）上的点突变后，重组菌株对氟喹诺酮会自然产生耐药性，而并不需要过度表达的外排泵。结论拓扑异构酶的突变在大肠埃希菌氟喹诺酮药物的耐药机制中起主要作用，对氟唪诺酮药物耐药的菌株通常廊同时具备gyrA和parC上的点突变。

Objective To characterize the roles of different quinolone resistance mechanisms in quinolone-resistant Escherichia coli isolates, including different topoisomerase point mutations, efflux pumps and outer membrane proteins. Methods Through homologous gene recombination methods, different quinolone-resistant mechanisms of E. coli mutants were constructed and the susceptibility changes of these mutants to different antimicrobials were measured. Results Efflux pumps AcrAB and outer membrane protein TolC played different roles in different E. coli isolates. Compared with other mechanisms, the mutations in topoisomerases played a dominant role in quinolone resistance. Only the mutations in parC had no effect on quinolone resistance, which further confirmed parC was the secondary target of quinolones in E. coli. Flu- oroquinolone susceptible E. coli would automatically become highly resistant to quinolones after acquiring the point mutations in both gyrA （S83L, D87N） and parC （S80I, A108V） , but not requiring the over-expression of efflux. Conclusion The mutations in topoisomerases play a dominant role in E. coli quinolone resistance, and the mutations in both gyrA and parC are required.