中文摘要：

目的了解枸橼酸杆菌中质粒介导喹诺酮耐药（PMQR）基因的分布，以期发现新型PMQR基因。测定临床分离的PMQR基因阳性枸橼酸杆菌对临床常用抗菌药物的敏感性。方法收集安徽医科大学第一附属医院检验科2009年临床分离的枸橼酸杆菌，PCR扩增qnr、nnr（6’）-Ib-cr和qepA基因，产物纯化测序，测序结果在GenBank上比对并行转移接合实验。对收集的PMQR基因阳性枸橼酸杆菌及其接合子，采用琼脂对倍稀释法进行临床常用抗菌药物的药物敏感试验。结果收集的枸橼酸杆菌共31株，8株菌株扩增出qnr，qnr基因阳性率为25．8％；其中6株扩增出qnrB。4株qnr阳性菌株的qnr基因转移接合成功。在qnr阳性的枸橼酸杆菌中，测序发现1种PMQR基因新亚型，命名为qnrB24。所有qnr阳性临床菌株对喹诺酮类药物的耐药率为87．5％，对头孢噻肟、阿米卡星、头孢他啶、头孢吡肟和庆大霉素的耐药率分别为75．0％、7．5％、62．5％、37．5％和87．5％，所有qnr阳性菌株对亚胺培南耐药表型为敏感。喹诺酮类药物对qnr阳性的接合子最低抑菌浓度升高10-23倍，敏感性下降。结论安徽地区枸橼酸杆菌中qnr基因型的检出率较高，以qnrB基因型为主，qnr阳性枸橼酸杆菌对常用抗菌药物耐药性较高。

英文摘要：

Objectives This study was conducted to detect and analyze the presence of plasmid mediated quinolone resistance （PMQR） determinants [qnr, aac- （6~）-Ib-cr and qepA] among clinical isolates of Citrobacter freundii strains isolated from patients in Anhui, China, and to understand the susceptibility of PMQR positive strains to commonly used antimicrobial agents. Methods During the year 2009, 31 Citrobacter strains were collected from the First Affiliated Hospital of Anhui Medical University. Polymerase chain reaction （PCR） was used to detect PMQR genes. Amplicons were purified, sequenced and compared with data from the GenBank. Conjugation experiments were conducted to determine whether the qnr-carrying plasmids were self-transferable. The susceptibility of the positive isolates and transconjugants were tested by agar dilution method according to Clinical and Laboratory Standards Institute （CLSI） guidelines. The minimum inhibitory concentrations （MIC） of ciprofloxacin and levofloxacin were determined by E-test strips. Results Among the 31 Citrobacter strains, the qnr genes were detected in 8 isolates （25.8%）, among which, 6 carried qnrB. Aac-（6＇）- Ib-cr and qepA were not identified in these isolates. The qnr genes were transferred from four clinical isolates to their transconjugants. Sequence analysis identified one novel qnrB variant （qnrB24）. The resistant rate of qnr-positive clinical isolates to quinolone was 87.5%. Most of them were also resistant to various other antibiotics, including cefotaxime （75.0 % ）, amikacin （7.5 % ）, ceftazidime （6 2.5 % ）, cefapime （37.5%）, and gentamycin （87.5 %）. All qnr positive strains were susceptible to imipenem. MIC of all transconjugants showed reduced susceptibility to {luoroquinolones, with MIC increased by 10 -- 23 folds. Conclusions Our study shows that qnr gene has occurred in Citrobacter freundii isolates from Anhui Province, China. QnrB is most prevalent in these isolates. Most qnr positive isolates are resistant to