Coban Ahmet Yılmaz, Nohut Okan Kadir, Tanrıverdi Çaycı Yeliz, Bayramoğlu Gülçin, Pirinççiler Müjgan, Cetinkaya Ebru, Cekiç Cihan Ciğdem, Bozdoğan Bülent, Durupınar Belma
Ondokuz Mayıs University Faculty of Medicine, Department of Medical Microbiology, Samsun, Turkey.
Mikrobiyol Bul. 2012 Jul;46(3):366-74.
Fluoroquinolones which are in use since 1986, are effective agents both against gram-positive and gram-negative bacteria. Quinolones show bactericidal effect as a result of inhibition of DNA gyrase and topoisomerase IV enzymes. Main quinolone resistance mechanisms are chromosomal mutations in these enzymes and decreased intracellular accumulation due to efflux pumps or decreased membrane uptake. Recently a new quinolone resistance mechanism mediated by plasmids has been defined. These plasmids carry genes called as qnr. Qnr genes do not cause quinolone resistance but they cause decreased quinolone susceptibility and lead to higher minimum inhibitory concentrations. Currently there are qnrA, qnrB, qnrC, qnrD and qnrS genes. This study was aimed to investigate the presence of plasmid-mediated quinolone resistance determinants in Enterobacteriaceae isolates collected from four different centers in Turkey. A total of 647 isolates (387 from Trabzon, Black Sea region; 82 from Canakkale, Trace region; 96 from Ankara, Central Anatolia region; 82 from Tokat, Black Sea region) belonging to the Enterobacteriaceae family collected between May-July 2009, were included in the study. Presence of qnrA, qnrB, qnrS and qnrC genes were investigated by multiplex polymerase chain reaction (PCR) method and confirmed by gene sequencing. The results of the PCR amplification revealed that 2 isolates were positive for qnrA, 12 isolates were positive for qnrB, 4 isolates were positive for qnrC and 10 isolates were positive for qnrS. However, the number of positive strains decreased with the use of gene sequencing, and this method led to the identification of qnrA1 in two isolates [Enterobacter cloacae (code. 796), Salmonella group B (code. 491)], qnrB1 in two isolates [Salmonella group B (code. 491), Citrobacter freundii (code. 768)], qnrB6 in one isolate [Escherichia coli (code. CC1800)], qnrB9 in one isolate [E.coli (code. CC1873)], qnrB24 in one isolate [Citrobacter koseri (code. MP5200)], qnrB27 in one isolate [C.freundii (code. 842)], qnrS1 in two isolates [E.coli (code. CC1705), E.coli (code.159)] and qnrB2 in one isolate [E.coli (code. 843)]. One of the isolates that carried the qnr gene was ciprofloxacin-resistant and two isolates were nalidixic-acid resistant. Transferable quinolone resistance due to the dissemination of qnr genes may have important impacts in terms of infection control and treatment problems. Survey of plasmid mediated quinolone resistance will help to determine the size of the issue and guide the measures that should be taken to avoid escalation of resistance and dissemination problem.
自1986年起开始使用的氟喹诺酮类药物，是对抗革兰氏阳性菌和革兰氏阴性菌的有效药剂。喹诺酮类药物通过抑制DNA回旋酶和拓扑异构酶IV发挥杀菌作用。主要的喹诺酮耐药机制是这些酶的染色体突变以及由于外排泵导致的细胞内蓄积减少或膜摄取减少。最近，一种由质粒介导的新喹诺酮耐药机制已被明确。这些质粒携带名为qnr的基因。Qnr基因不会导致喹诺酮耐药，但会导致喹诺酮敏感性降低并导致更高的最低抑菌浓度。目前有qnrA、qnrB、qnrC、qnrD和qnrS基因。本研究旨在调查从土耳其四个不同中心收集的肠杆菌科分离株中质粒介导的喹诺酮耐药决定因素的存在情况。2009年5月至7月间收集的总共647株属于肠杆菌科的分离株（387株来自黑海地区的特拉布宗；82株来自色雷斯地区的恰纳卡莱；96株来自安纳托利亚中部地区的安卡拉；82株来自黑海地区的托卡特）被纳入研究。通过多重聚合酶链反应（PCR）方法研究qnrA、qnrB、qnrS和qnrC基因的存在情况，并通过基因测序进行确认。PCR扩增结果显示，2株分离株qnrA呈阳性，12株分离株qnrB呈阳性，4株分离株qnrC呈阳性，10株分离株qnrS呈阳性。然而，随着基因测序的使用，阳性菌株数量减少，该方法导致在2株分离株中鉴定出qnrA1[阴沟肠杆菌（编号796），B群沙门氏菌（编号491）]，2株分离株中鉴定出qnrB1[B群沙门氏菌（编号491），弗氏柠檬酸杆菌（编号768）]，1株分离株中鉴定出qnrB6[大肠杆菌（编号CC1800）]，1株分离株中鉴定出qnrB9[大肠杆菌（编号CC1873）]，1株分离株中鉴定出qnrB24[科氏柠檬酸杆菌（编号MP5200）]，1株分离株中鉴定出qnrB27[弗氏柠檬酸杆菌（编号842）]，2株分离株中鉴定出qnrS1[大肠杆菌（编号CC1705），大肠杆菌（编号159）]，1株分离株中鉴定出qnrB2[大肠杆菌（编号843）]。携带qnr基因的分离株中有1株对环丙沙星耐药，2株对萘啶酸耐药。由于qnr基因的传播导致的可转移喹诺酮耐药性在感染控制和治疗问题方面可能产生重要影响。对质粒介导的喹诺酮耐药性的调查将有助于确定问题的规模，并指导应采取的措施以避免耐药性升级和传播问题。
