男性泌尿系统感染产超广谱β-内酰胺酶和AmpC酶的大肠埃希菌基因分型研究

目的:了解本院男性泌尿系感染产超广谱β-内酰胺酶(ESBLs)和AmpC酶大肠埃希菌(E.coli)的基因型分布。方法:收集2004年1月~2005年6月本院临床分离的尿培养阳性大肠埃希菌共187株,用CLSI/NCCLS推荐的纸片扩散法(包括筛选和确认实验)进行耐药表型检测,三维酶试验检测ESBLs和AmpC酶,PCR扩增质粒型ESBLs和ampC基因,肉汤交配法检测质粒型ampC基因的接合传递性。结果:产ESBLs大肠埃希菌检出率为24.6%(46/187)。在三维试验中,46株均产分解头孢三嗪(CRO)的β-内酰胺酶,其中3株产ESBLs和AmpC两种酶,其余43株单产ESBLs酶。在PCR扩增试验中,44株扩增出ESBLs基因b laTEM、b laCTX-M、b laOXA3型中的1型或1型以上基因片段,未扩增出b laSHV型基因片段;3株扩增出质粒介导的ampC基因,2株为C IT型,1株为DHA型。携带质粒型ampC基因的菌株均将耐药性传递给受体菌。结论:南京地区男性泌尿系感染产ESBLs大肠埃希菌以CTX-M型为主;质粒介导AmpC酶已在大肠埃希菌中出现,其耐药性能够水平传播,给临床抗感染治疗带来严重威胁。

Genotype Distribution of Extended-spectrum β-lactamases and AmpC β-lactamases Produced in Escherichia Coli Isolated from Men with Urinary Infection

OBJECTIVE: To study the genotype distribution of extended-spectrum p-lactamases (ESBLs) and AmpC p-lactamases produced in E. coli isolated from men with urinary infection in Nanjing. METHODS: Organisms of clinical infection were identified by automatic microbial system (Vitek-32). ESBLs were detected by disk diffusion confirmatory test, and ESBLs and AmpC p-lactamases by three-dimensional extract test (TDET) , the presence of plasmid-mediated ESBLs and ampC genes determined by PCR, and conjugal transfer assays of the ampC resistance determinants carried out by a broth mating procedure. RESULTS: ESBLs were produced in 24. 6% (46/187) of the E. coli and the 46 E. coli isolates showed p-lactamase activity in TDET, 3 positive for both ESBLs and AmpC beta-lactamases and 43 for ESBLs only. Forty-four of the 46 isolates were shown by PCR to contain at least one of the genes blaTEM, blaOXA, bla(CTX-M), but no blaSHA. AmpC specific amplication products were observed in 3 of the 46 isolates, of which 2 were of CIT type, and 1 of DHA type. All of the 3 transconjugants transferred the plasmids harbouring ampC genes to recipients. CONCLUSION: CTX-M is the most common genotype in plasmid-mediated ESBLs produced by E. coli isolated from men with urinary infection in Nanjing. Present findings indicate that AmpC-producing E. coli are present in this hospital, and ampC-encoding plasmids are transferable.