鼠伤寒沙门菌临床分离株对喹诺酮类药物耐药机制的研究

目的 研究引起儿童腹泻鼠伤寒沙门菌对喹诺酮类抗菌药物的耐药机制.方法 采用K-B法测定62株鼠伤寒沙门菌对常用抗菌药物的敏感性；应用PCR法和DNA测序法检测喹诺酮耐药决定区(QRDRs)和质粒介导的喹诺酮耐药基因；采用接合试验测定耐药基因的转移性；PFGE法测定耐药菌株的同源性.结果 62株肠伤寒沙门菌中有40株对环丙沙星耐药(MIC≥0.5 μg/ml),其中28株为低水平耐药,12株为高水平耐药,且所有对环丙沙星耐药菌株同时对其他多种抗菌药物耐药；40株环丙沙星耐药菌株分属于4种PFGE型,分别是A型7株、B型4株、E型1株、D型28株；两株对环丙沙星高水平耐药菌株同时存在gyrA和parC两个位点的突变,其余环丙沙星耐药菌株仅发现gyrA 1个位点的突变,未检测到qnr和qepA基因；62株鼠伤寒沙门菌中有23株为aac-(6′)-Ib-cr阳性,其中19株PFGE分型为D型.结论 腹泻患儿分离的肠伤寒沙门菌对环丙沙星耐药率高,喹诺耐耐药决定区gyrA基因的点突变和携带aac-(6′) -Ib-cr基因是导致鼠伤寒沙门菌对环丙沙星耐药的主要原因.

Study on quinolones-resistance mechanism of clinical isolates of Salmonella enterica typhimurium

OBJECTIVE To study the quinolones-resistance mechanism of Salmonella enterica typhimurium causing diarrhea of the hospitalized pediatric patients.METHODS Antimicrobial susceptibility testing for 62 strains of S.enterical typhimurium was performed by disk diffusion.PCR was used for detecting point mutations in quinolone resistance-determining regions(QRDRs) and plasmid-mediated qninolone resistance determinants.The transfer of ciprofloxacin resistance was determined by conjugation.PFGE was performed for determining the homogeneity of the isolates with ciprofloxacin resistance.RESULTS Totally 40(64.5%) of 62 S.enterica typhimurium isolates were resistant to ciprofloxacin(MIC≥ 0.5 μg/ml),among which 28 isolates were with low-level ciprofloxacin resistance and 12 isolates with high-level ciprofloxacin resistance.All ciprofloxacin-resistant isolates were multidrug-resistant to other antimicrobial agents;totally four PFGE clusters were found in 40 ciprofloxacin-resistant isolates,among which there were 7 strains of PFGE cluster A,4 strains of PFGE cluster B,1 strain of PFGE cluster E and 28 strains of PFGE cluster D;two isolates with high-level ciprofloxacin resistance had 2 mutations in QRDRs of gyrA and parC.The remaining ciprofloxacin-resistant isolates had only one mutation in QRDRs of gyrA.All 62 S.enterica typhimurium isolates were negative for qnr genes and qepA.Totally 23(37.1%) out of 62 isolates tested were positive for aac-(6’)-Ib-cr.Nineteen isolates harboring aac-(6’)-Ib-cr belonged to PFGE cluster D.CONCLUSION There is high prevalence of ciprofloxacin resistance and aac-(6’)-Ib-cr detected in S.enterica typhimurium isolates from the hospitalized pediatric patients with diarrhea.Single mutation in gyrA of QRDRs and its carrying with aac-(6’)-Ib-cr are attributed to the ciprofloxacin resistance of S.enterica typhimurium.