大肠埃希菌尿液分离株中检出gyrA基因新变异株

目的 调查大肠埃希菌尿液分离株中喹诺酮类耐药相关基因的存在与变化状况.方法 收集宁波市第一医院2008年10月到2009年3月患者尿液标本中分离的大肠埃希菌共28株,采用聚合酶链反应(PCR)及序列分析的方法分析1种染色体介导的喹诺酮类耐药相关基因(gyrA基因)和5种质粒介导的喹诺酮类耐药相关基因qnrA、qnrB、qnrS、aac(6＇)-Ⅰb、qepA].结果 28株大肠埃希菌检测到1株aac(6＇)-Ⅰb-Cr基因阳性株(经测序比对证实),qnrA、qnrB、qnrS、qepA基因均未检出.gyrA基因83位密码子28株菌都有突变(100.0%),其突变方式为TCG-83→HTG,导致氨基酸从丝氨酸(S)-83→亮氨酸(L);87位密码子22株菌(78.6%)有突变,可分为两种突变方式:21株(75.0%)突变方式为GAC-87→AAC,导致氨基酸从天冬氨酸(D)-87→天冬酰胺(N);5号株gyrA基因(3.6%)为新亚型,其突变方式为GAC-87→TAC,导致氨基酸从天冬氨酸(D)-87→脯氨酸(Y),另6株菌87位密码子无突变.结论 本组大肠埃希菌gyrA基因突变率为100.0%,是喹诺酮类耐药的主要原因.其他耐药相关基因阳性率很低.

New subtype of gyrA gene in multi-drug resistant strains of Escherichia coli isolated from urine

Objective To investigate the distribution and variety of quinolone-resistance genes in multi-drug resistant strains of Escherichia coli (E. coli) isolated from urine. Methods From October 2008 to March 2009, 28 strains of multi-drug resistant E. coli isolated from urine were collected from Ningbo No. 1 Hospital, China. One kind of chromosome-mediated quinolone-resistance gene(gyrA) and 5 kinds of plas-mid-mediated quinolone-resistance genesqnrA, qnrB, qnrS, aac(6')- Ⅰb-Cr, qepA]were analyzed by PCR and verificated by DNA sequencing. Results In 28 strains ofE. coli, only 1 strain was detected to harbor aac(6')-Ⅰb-Or (confirmed by DNA sequencing and genomic comparison with sequence registered in NC-BI), but qnrA, qnrB, qnrS, qepA could not be detected. Furthermore, all 28 strains(100.0%) contained mutations at 83rd coden in gyrA: TCG→TTG(mutations at 83rd amino acid: S83L). However, 22 strains (78.6%) contained mutation at 87th ceden in gyrA. Among them, 21 strains(75.0% ) contained muta-tions: GAC→AAC(mutations at 87th amino acid: D87N) ; while gyrA gene of NB005 (3.6%) contained mutations: GAC→TAC(mutations at 87th amino acid: D87Y), which was a new subtype(GenBank Acces-sion No. GQ286174). And other 6 strains contained no mutation at 87th coden. Conclusion All isolates of E. coli contained mutations in gyrA(100.0%), which play a key role in resistance to quinolones antimi-crobial agents, but positive rate of other resistance genes is low.