鼠伤寒沙门菌对喹诺酮类耐药机制的研究

Study on the mechanism of resistance to quinolones in Salmonella typhimurium

目的检测鼠伤寒沙门菌（STM）对喹诺酮类药物的耐药性及耐药机制的分析。方法收集2004年7月1日-10月31日武汉地区4所大型医院的门诊腹泻病人的粪便进行分离培养出鼠伤寒沙门菌33株。琼脂稀释法测其对喹诺酮类药物的MIC，并抽提此菌的基因组DNA，用PCR方法检测喹诺酮类抗菌药作用于鼠伤寒沙门菌的靶位点：Ⅱ型拓扑异构酶，即DNA促旋酶和拓扑异构酶Ⅳ上的基因片段（gyrA，gyrB，parC，parE）突变情况。结果33株鼠伤寒沙门菌中有24株对环丙沙星产生了很强的耐药性（MIC值4～16mg／L），耐药率达72．7％。24株耐药株中gyrA和parC的突变比较常见，其中gyrA位点都存在突变点，且双重突变占92％，并协同parC的点突变造成高水平的耐药；gyrB和parE的突变很少见，本研究中有少数高水平耐药株的parE和gyrB位点发现可疑的碱基插入。结论研究结果表明武汉地区社区内鼠伤寒沙门菌感染对喹诺酮类药物的耐药性严重，其主要机制是喹诺酮类耐药决定区（QRDR）的基因突变，特别是多个位点同时突变导致高水平耐药。

Objective To investigate the resistance of Salmonella typhimurium （STM） to quinolones and its mechanism. Methods A total of 33 S. typhimurium strains resistant to ciprofloxacin were isolated from stool of outpatients from four hospitals in Wuhan between July 1, 2004 and October 31, 2004. Antibiotic susceptibility of the isolates was evaluated by the agar dilution method. And all of the isolates were studied for mutations in the genes encoding gyrase （gyrA and gyrB） and topoisomerase Ⅳ （parC and parE） by PCR amplification. Results About 72.7 % （24/33） of the isolates were highly resistant to ciprofloxacin （MIC： 4 to 16 mg/L）. Mutation was common in gyrA and parC genes in the 24 ciprofloxacin-resistant strains. Mutation in gyrA gene was identified in all quinolone-resistant strains. Double-point mutation accounted for 92 % of gyrA mutation. This mutation together with parC mutation resulted in high level resistance. Few mutations were found in gyrB and pare genes. Some base insert was found at positions of gyrB and parE genes in a few highly resistant strains. Conclusions The study suggests that the resistance in S. typhimurium isolates from community infections is very serious in Wuhan. The resistance is associated with mutations of quinolone resistance-determining regions, especially multiple mutations.