parC基因突变致环丙沙星不敏感化脓性链球菌及其同源性研究

Ciprofloxacin non-susceptible Streptococcus pyogenes due to mutations in parC gene and its homology analysis

目的研究环丙沙星不敏感化脓性链球菌的耐药机制及其同源性。方法对2012年3月北京地区分离自猩红热患者的48株化脓性链球菌采用稀释法检测环丙沙星及临床常用7种抗生素的MIC。对环丙沙星MIC≥4mg／L的13株化脓性链球菌检测氟喹诺酮染色体介导的耐药基因gyrA，gyrB，parC，parE的突变，同时以环丙沙星MIC40．25mg／L的4株化脓性链球菌做比对。采用脉冲场凝胶电泳（PFGE）对分离自北京不同地区的菌株进行同源性分析。结果化脓性链球菌对左氧氟沙星、氨苄西林和青霉素的敏感率均为100％。对四环素、红霉素和克林霉素的耐药率分别为91．7％（44／48）、91．7％（44／48）和89．6％（43／48）。环丙沙星、左氧氟沙星和莫西沙星的MIC50分别为2mg／L、1mg／L和40．25mg／L；MIC90分别为4mg／L、2mg／L和0．5mg／L。48株化脓性链球菌中有12株对环丙沙星MIC为4mg／L，1株MIC为8mg／L，菌株来自北京朝阳区。对这13株耐药基因检测结果显示，12株在parC基因上出现79位丝氨酸突变为苯丙氨酸或酪氨酸（Ser79Phe／Tyr），10株在parG基因的121位出现丙氨酸突变为缬氨酸（Ala121Val）。发现1株在parC基因上Ser79Phe突变合并parE基因上371位丝氨酸突变为亮氨酸（Ser371Leu）的化脓性链球菌，但该菌株对环丙沙星的MIC未显著增高（MIC=4mg／L）。17株试验菌株的PFGE结果显示为7个克隆，其中克隆A均为环丙沙星MIC≥4mg／L的菌株，主要分布在朝阳区、大兴区、丰台区、顺义区和石景山区，占MIC≥4mg／L菌株的69．2％。克隆c菌株也为环丙沙星MIC94mg／L菌株，均分布在怀柔区。克隆B、D、E、F和G分别分散在不同地区。结论parC基因突变是北京地区分离的化脓性链球菌对环丙沙星MIC略有升高的主要原因，PFGE分析显示化脓性链球菌感染在北京部分地区有小范围流行。

Objective To investigate the resistant mechanism of Streptococcus pyogenes to ciprofloxacin and its homology. Methods Forty-eight isolates of Streptococcus pyogenes were collected from patients diagnosed with scarfiet fever in districts of Beijing in March ,2012 and MIC to ciprofloxacin and other 7 common antibiotics in clinic were detected by using blood M-H agar dilution method. Thirteen isolates, which have MICs≥4 rag/L against ciprofloxacin, were detected for mutations of Fluoroquinolone resistance genes gyrA, gyrB, parC, parE. At the same time, 4 isolates, with MIC ≤0. 25 mg/L against ciprofloxacin, were used for comparison. Homology analysis of 17 isolates from different areas of Beijing was performed by using the method of pulsed field gel electrophoresis. Results Sensitive rates of Streptococcus pyogenes to levofloxacin, ampicillin and penicillin were all 100%. The resistance rates to tetracycline, erythromycin and clindamycin were 91.7% （ 44/48 ） , 91.7% （ 44/48 ） and 89.6% （ 43/48 ） , respectively. MICso of eiprofloxacin, levofloxacin and moxifloxacin was 2 mg/L , 1 mg/L and ≤0. 25 mg/L, respectively; MICgo was 4 mg/L,2 mg/L and 0. 5 mg/L, respectively. Of the 48 isolates of Streptococcus pyogenes, 12 isolates showed the MIC at 4 rag/L, while one isolate has a MIC against ciprof/oxacin at 8 mg/L, which isolated from Chaoyang district. Analysis of sequence of chromosome mediated fluoroquinolone resistance genes in those 13 ciprofloxaein non-susceptible isolates exhibited that there were 12 isolates that harbored Ser79Phc/Tyr mutation and 10 isolates harbored Alal21Val in parC gene. It is shown that one isolate contained Ser79Phe mutation in parC gene in the occurring of Ser371Leu mutation in parE gene for the first time, but there was no marked increase in ciprofloxacin MIC （MIC=4 mg/L）. There were no mutations in gyrA and gyrB genes. The PFGE results demonstrated that the 17 tested isolates could be divided into 7 clones. The clone A isolates from Chaoyang, Daxing , Fengtai, Shunyi and Shijingshan district have a MIC ≥4 mg/L against ciprofloxacin, which covered 69.2% of all MIC ≥4 mg/L isolates. The clone C isolates from Huairou district were MIC ≥4 mg/L isolates. B, D, E, F and G clones isolates come from different districts. Conclusions The mutation of parC gene was the main reason that contribute to the slightly increase of ciprofloxacin MIC in Streptococcus pyogenes isolated from Beijing. The PFGE analysis showed that there was a small scale prevalence caused by the infection of Streptococcus pyogenes in some districts.