CTX—M型超广谱β内酰胺酶肺炎克雷伯菌的分子流行病学研究

目的了解湖北地区产CTX—M型超广谱β内酰胺酶（ESBLs）肺炎克雷伯菌的流行基因型，为有效预防和控制该类感染提供理论依据。方法临床分离的无重复产ESBLs的肺炎克雷伯菌70株，采用NCCLS表型筛选和确证试验检测ESBLs，采用聚合酶链反应（PCR）检测CTX—M基因型，并采用PCR—RFLP检测blaCTX—M基因分型，质粒接合试验探讨产CTX—M型ESBLs菌株的传播机制。结果70株产ESBLs的肺炎克雷伯菌中，产CTX—M基N型的肺炎克雷伯菌有26株（37％），PCR-RFLP及DNA测序证实其均为CTX—M-1亚组，其中CTX—M-3型最常见，质粒接合试验证实CTX—M型ESBLs介导的耐药可以水平转移。结论湖北地区存在着CTX—M基因的流行，且产CTX—M型ESBLs菌株的传播机制以质粒介导的为主，可以水平传播，应加强湖北地区产CTX—M型ESBLs菌株的分子流行病学检测。     

产超广谱β内酰胺酶大肠埃希菌与肺炎克雷伯菌的基因型和耐药性分析

目的研究我院住院患儿分离产ESBLs大肠埃希菌及肺炎克雷伯菌的基因型及其相关耐药性分析。方法收集2004年10月-2005年10月我院住院患儿呼吸道分离产ESBLs大肠埃希菌75株，肺炎克雷伯菌45株，PCR限制性片段长度多态性（RFLP）分析及PCR产物克隆测序等方法明确ESBLs基因型，并结合体外抗生素敏感试验研究基因分型与细菌对不同头孢菌素及氨曲南的敏感性的关系。结果上述120株细菌中112株（93．3％）产CTX—M型p内酰胺酶；未能扩增出SHV型、TEM型ESBL基因。CTX—M型基因亚型主要为CTX—M9簇中的CTX—M-14型（78、6％），其次为CTX—M-1簇中的CTX—M-3型（19．6％），仅有1．8％为CTX—M-8型；携带CTX-M-1簇的菌株对头孢他啶、头孢哌酮-舒巴坦、阿莫西林-克拉维酸、头孢吡肟及氨曲南的耐药率均明显高于CTX—M-9型。结论CTX—M基因型为武汉地区儿童分离大肠埃希菌以及肺炎克雷伯菌中最常见的ESBLs，CTX—M-14为最常见基因型，其次为CTX—M-3型；CTX—M-9簇及CTX-M-1簇对头孢他啶、头孢吡肟、头孢哌酮-舒巴坦和氨曲南的水解能力差异明显。     

产超广谱β内酰胺酶49株细菌耐药基因调查

目的 了解49株产超广谱β内酰胺酶（ESBLs）细菌的耐药基因。方法 采用纸片扩散法检测产ESBLs细菌，通过基因扩增、序列分析、脉冲场凝胶电泳技术研究ESBLs基因型以及产ESBLs细菌同源性。结果 产ESBLs大肠埃希菌、肺炎克雷伯菌、产酸克雷伯菌流行率自2000年的20％，增长至2003年的40％。49株产ESBLs细菌中，以CTX-M-14（n=33）亚型最常见，其他亚型包括CTX-M-3、CTX-M-9、CTX-M-12、CTX-M-15、CTX-M-24、SHV-5a，1株细菌同时产CTX—M-3、CTX—M-14两种CTX-M型ESBLs；4株表型确证试验阳性细菌未能分型。除2株大肠埃希菌、2株肺炎克雷伯菌有亲缘性外，其他菌株间无同源性。结论 产ESBLs细菌分离率逐年增高，以CTX—M型酶为主。PFGE试验证明非流行所致。     

CTX-M型超广谱β内酰胺酶肺炎克雷伯菌的分子流行病学研究

目的了解湖北地区产CTX—M型超广谱β内酰胺酶（ESBLs）肺炎克雷伯菌的流行基因型，为有效预防和控制该类感染提供理论依据。方法临床分离的无重复产ESBLs的肺炎克雷伯菌70株，采用NCCLS表型筛选和确证试验检测ESBLs，采用聚合酶链反应（PCR）检测CTX—M基因型，并采用PCR—RFLP检测blaCTX—M基因分型，质粒接合试验探讨产CTX—M型ESBLs菌株的传播机制。结果70株产ESBLs的肺炎克雷伯菌中，产CTX—M基N型的肺炎克雷伯菌有26株（37％），PCR-RFLP及DNA测序证实其均为CTX—M-1亚组，其中CTX—M-3型最常见，质粒接合试验证实CTX—M型ESBLs介导的耐药可以水平转移。结论湖北地区存在着CTX—M基因的流行，且产CTX—M型ESBLs菌株的传播机制以质粒介导的为主，可以水平传播，应加强湖北地区产CTX—M型ESBLs菌株的分子流行病学检测。     

产超广谱β-内酰胺酶肺炎克雷伯菌基因型研究

目的：研究医院感染超广谱β-内酰胺酶（ESBLs）肺炎克雷伯菌的基因型。方法：收集分离鉴定菌株，通过K—B法药敏实验初筛以确认产ESBLs菌株，并对ESBLs基因进行初步分型。结果：17株肺炎克雷伯菌产生的ESBLs以CTX-M-3、CTX-M-15、CTX-M-22为主要基因型，其中8株为CTX—M-3型；6株为CTX-M-22型；1株为CTX-M-15型；1株同时产CTX-M-3、CTX-M-22；1株同时产CTX-M-15、CTX-M-22型。结论：我院肺炎克雷伯菌临床分离株中的ESBLs基因型以CTX-M型酶为主。     

产超广谱β-内酰胺酶的肺炎克雷伯菌相关耐药基因研究

目的了解常州地区肺炎克雷伯菌耐药状况及β-内酰胺类耐药基因。方法用琼脂稀释法检测氨苄西林、哌拉西林、哌拉西林-他唑巴坦、头孢噻肟、头孢他啶、头孢吡肟、氨曲南和亚胺培南对肺炎克雷伯菌的最低抑菌浓度（MIC）。采用聚合酶链反应（PCR）检测产超广谱β-内酰胺酶（ESBLs）肺炎克雷伯菌16种相关耐药基因,并用DNA测序仪测序。结果120株肺炎克雷伯菌ESBLs阳性率为44．2％（53株）。从53株肺炎克雷伯菌中检出TEM、SHV、CTX—M-1群、CTX—M-9群、OXA-1群、LEN、OKP和DHA8种β-内酰胺酶基因,阳性率分别为75．5％、22．6％、18．9％、7．5％、11．3％、5．7％、3．8％和41．5％,其中2株菌同时检出6种B-内酰胺酶基因。基因测序证实为TEM-1、TEM-11、SHV-13、SHV．28、CTX—M-22、CTX—M-55、OXA-1和OKP-6等。结论本地区肺炎克雷伯菌已携带多种β-内酰胺酶耐药基因,是其对β-内酰胺类抗菌药物耐药的重要原因之一。     

武汉市儿童医院临床分离大肠埃希菌与肺炎克雷伯菌中产质粒介导AmpC酶和ESBLs的研究

目的研究武汉市儿童医院临床分离高产质粒AmpC酶和超超广谱β内酰胺酶（SSBL）肺炎克雷伯菌与大肠埃希菌的分子流行病学特征。方法收集我院2005年8月-2006年8月住院患儿临床分离的头孢西丁中介或耐药的大肠埃希菌和肺炎克雷伯菌161株。采用三维试验检测AmpC酶，表型确认试验检测ESBLs，质粒转化试验定位耐药基因；采用PCR技术扩增质粒AmpC与CTX—M基因；使用限制性片段长度多态性（RFLP）技术确定CTX—M基因簇的特征；利用基因测序确定AmpC酶及CTX—M的基因亚型。结果DHA-1型和ACT-1型为主要的质粒AmpC酶基因型，发现1种新的ACT型质粒AmpC酶，其与ACT-1的同源性仅为84％。CTX—M-14型和CTX-M-3型为主要的ESBLs基因型。最常见的大肠埃希菌SSBL基因组合为CTX-M-14＋DHA-1＋ACT-1型，肺炎克雷伯菌的为CTX—M-3＋DHA-1＋ACT-1。结论我院临床分离的肺炎克雷伯菌和大肠埃希菌中，产SSBL菌株所占比例显著高于单产质粒AmpC酶菌株；CTXM-14／CTX—M-3＋DHA-1＋ACT-1是大肠埃希菌和肺炎克雷伯菌中最常见的SSBL基因型。     

多重耐药肺炎克雷伯菌基因型和整合子的分析

目的了解多重耐药肺炎克雷伯菌的基因型和整合子存在情况。方法设计TEM、SHV和CTX-M型及Ⅰ、Ⅱ、Ⅲ类整合酶基因特异性引物,并将聚合酶链反应（PCR）扩增获得哥内酰胺酶编码基因,分别克隆入pMD18-T载体后测定其核苷酸序列,分析其基因亚型。结果该多重耐药株与TEM-1、SHV-12及CTX—M-3型编码基因序列的同源性为100％,Ⅰ类整合酶基因检测阳性,Ⅱ、Ⅲ类整合酶基因检测阴性。结论Ⅰ类整合子存在产ESBLs肺炎克雷伯菌中。     

广州地区肺炎克雷伯菌携带CTX-M-14质粒同源性分析

目的研究广州肺炎克雷伯菌(Klebsiella pneumonia,Kp)CTX-M-14型超广谱β-内酰胺酶(ESBLs)的质粒同源性特征。方法收集2007～2008年广州地区9家医院临床分离的产ESBLs肺炎克雷伯菌,PCR检测ESBLs分子表型;用肠杆菌科基因间重复序列PCR(Enterobacteriaceae repetive intergenic consensus-PCR,ERIC-PCR)分析产CTX-M-14型ESBLs菌株的分子同源性;取产CTX-M-14型ESBLs的Kp的所有非克隆株,通过结合试验、质粒图谱、PCR分析blaCTX-M-14基因环境。结果产ESBLsKp共181株,69.1%(125/181)的产ESBLs株为CTX-M表型;其中产CTX-M-14型ESBLs株的检出率为28.2%(51/181),经ERIC-PCR分析,共分为33个基因型;基因环境显示,75.7%(25/33)blaCTX-M-14位于90 kb的可接合质粒上,其他耐药基因blaSHV、blaDHA-1、blaOXA-1、qnr、aac(6’)-Ib-cr等均未检到;有28株菌的blaCTX-M-14位于ISEcp1-like插入序列下游,ISEcp1-like末端与blaCTX-M-14间距均为42 bp,有2株菌ISEcp1末端与blaCTX-M-14起始区间距也为42 bp;但在ISECP1中间有一个S10插入序列。结论广州地区ESBLs主要分子表型为CTX-M型,主要流行为CTX-M-14型,携blaCTX-M-14质粒的传播,可能是本地区CTX-M型ESBLs高发生率的主要原因。     

复合转座子ISEcp1B与IS903介导CTX-M ESBLs新基因亚型传播机制的研究

目的研究肺炎克雷伯菌Kp49,CTX-M型超广谱β-内酰胺酶(ESBLs)新亚型的基因环境,并分析其传播的分子机制。方法用K-B药敏法分析肺炎克雷伯菌Kp49的耐药性;用多重聚合酶链反应(PCR)技术扩增CTX-M-G1、TEM、SHV、DHA、ACT、IMP-1、VIM-1、ISEcp1B、IS903及Ⅰ类整合子,PCR扩增ISEcp1B下游的CTX-M型ESBLs全序列并测序。结果肺炎克雷伯菌Kp49只对亚胺培南敏感,对其余21种抗菌剂均耐药。检出TEM、SHV、CTX-M-G1及DHA基因Ⅰ类整合子。检出1种新的CTX-M ESBLs基因亚型,全长876 bp,与blaTX-M-14相比有1个核苷酸不同(GenBank登陆号:EF446126)。blaCTX-M-like的上游是ISEcp1B的遗传元件,下游是插入序列IS903的保守序列组成复合转座子。可能是ISEcp1B序列通过转座子机制俘获β-内酰胺酶,并提供-35及-10位点2个启动子,对下游CTX-M型ESBLs的高水平表达起重要的调控作用。结论插入序列ISEcp1B与IS903组成的复合转座子可能介导了新的CTX-M ESBLs基因亚型的水平传播,并驱使其高度表达,使Kp49对多种抗菌剂耐药。     

广州地区产CTX-M型超广谱β内酰胺酶大肠埃希菌和肺炎克雷伯菌的研究

目的 研究广州地区大肠埃希菌和肺炎克雷伯菌CTX-M型超广谱β内酰胺酶(ESBLs)的分子表型、流行病学和耐药基因环境特征.方法 收集2007-2008年广州地区9家医院临床分离产ESBLs的181株大肠埃希菌和180株肺炎克雷伯菌,通过PCR检测ESBLs分子表型;通过接合试验、质粒图谱、PCR分析CTX-M-15型ESBLs的基因环境,肠杆菌科基因间重复序列引物PCR(ERIC-PCR)分析产CTX-M-15型ESBLs菌株的分子同源性.结果 67.3%(243/361)的ESBLs产生株为CTX-M表型,其中CTX-M-1群和CTX-M-9群各占46.9%(114/243)和53.1%(129/243),未发现其他CTX-M亚群.CTX-M-14和CTXM-15是最常见的ESBLs基因型,其中CTX-M-14在大肠埃希菌和肺炎克雷伯菌的检出率分别35.4%(64/181)和28.3%(51/180),CTX-M-15在这两种菌的检出率分别为21.5%(39/181)和26.1%(47/180),此外还检出对头孢他啶有水解活性的CTX-M-55、CTX-M-19和CTX-M-27.采用ERIC-PER分析CTX-M-15产生株的同源性,39株大肠埃希菌被分为28个基因型,47株肺炎克雷伯菌被分为30个基因型.67.6%(25/37)和32.4%(12/37)bla相似文献   

A novel ceftazidime-hydrolysing extended-spectrum beta-lactamase, CTX-M-54, with a single amino acid substitution at position 167 in the omega loop

OBJECTIVES: To characterize a novel ceftazidime-hydrolysing CTX-M mutant, designated CTX-M-54, produced by Klebsiella pneumoniae clinical isolate BDK0419 and to investigate its genetic environment. METHODS: Antimicrobial susceptibilities were determined by disc diffusion and agar dilution methods, and the double-disc synergy test was carried out. Detection of genes encoding class A beta-lactamases was performed by PCR amplification, and the genetic organization of the blaCTX-M-54 gene was investigated by PCR and sequencing of the regions surrounding this gene. Kinetic parameters were determined from purified CTX-M-54. RESULTS: The strain BDK0419 contained a transferable plasmid with a molecular size of approximately 21 kbp that carries both blaSHV-2a and blaCTX-M-54 beta-lactamase genes, along with two other plasmids. The blaCTX-M-54 gene was flanked upstream by an ISEcp1 insertion sequence and downstream by an IS903-like element. CTX-M-54 had a P167Q substitution within the omega loop region of class A beta-lactamases compared with the sequence of CTX-M-3. The MIC of ceftazidime for K. pneumoniae BDK0419 was 16-fold higher than that of cefotaxime; however, the kinetic parameter of CTX-M-54 against ceftazidime revealed a low catalytic efficiency. CONCLUSIONS: This work shows once again that novel CTX-M enzymes with an expanded activity towards ceftazidime through a single amino acid substitution can be identified from clinical isolates. Thus, detection of CTX-M enzymes can no longer be based solely on the resistance phenotypes of clinical isolates towards ceftazidime and cefotaxime.     

腹腔感染患者大肠埃希菌超广谱β-内酰胺酶及整合子研究

目的了解腹腔感染患者大肠埃希菌超广谱β-内酰胺酶(ESBLs)及Ⅰ、Ⅱ类整合子的分布情况。方法共收集分离自腹腔感染患者的大肠埃希菌62株,纸片扩散法测定16种抗菌药物敏感性,采用纸片协同扩散法检测ESBLs表型,PCR检测blaCTX-M、blaSHV、blaTEM及Ⅰ、Ⅱ类整合子基因,整合子阳性菌株进一步检测整合子的可变区基因盒。结果大肠埃希菌对碳青霉烯类、哌拉西林/他唑巴坦100%敏感,对复方磺胺甲噁唑耐药率最高(62.9%)。30株大肠埃希菌产ESBLs,其中基因型blaCTX-M-14、blaCTX-M-3、blaTEM-1、blaCTX-M-14+TEM-1分别检出16株、4株、3株、7株。未发现携带SHV型ESBLs菌株。有40株(64.5%)大肠埃希菌携带Ⅰ类整合子,其中1株同时携带Ⅰ、Ⅱ类整合子,共扩增出7种耐药基因盒组合形式。最常见的基因盒组合为dfrA17-aadA5,其次为dfrA12-orfF-aadA2,Ⅱ类整合子携带dfrA1-sat1-aadA1。结论腹腔感染大肠埃希菌主要携带blaCTX-M-14和blaTEM-1,Ⅰ类整合子的存在非常普遍,主要介导对氨基糖苷类及磺胺类耐药。     

广州地区产CTX-M型超广谱β内酰胺酶大肠埃希菌和肺炎克雷伯菌的研究

目的 研究广州地区大肠埃希菌和肺炎克雷伯菌CTX-M型超广谱β内酰胺酶(ESBLs)的分子表型、流行病学和耐药基因环境特征.方法 收集2007-2008年广州地区9家医院临床分离产ESBLs的181株大肠埃希菌和180株肺炎克雷伯菌,通过PCR检测ESBLs分子表型;通过接合试验、质粒图谱、PCR分析CTX-M-15型ESBLs的基因环境,肠杆菌科基因间重复序列引物PCR(ERIC-PCR)分析产CTX-M-15型ESBLs菌株的分子同源性.结果 67.3%(243/361)的ESBLs产生株为CTX-M表型,其中CTX-M-1群和CTX-M-9群各占46.9%(114/243)和53.1%(129/243),未发现其他CTX-M亚群.CTX-M-14和CTXM-15是最常见的ESBLs基因型,其中CTX-M-14在大肠埃希菌和肺炎克雷伯菌的检出率分别35.4%(64/181)和28.3%(51/180),CTX-M-15在这两种菌的检出率分别为21.5%(39/181)和26.1%(47/180),此外还检出对头孢他啶有水解活性的CTX-M-55、CTX-M-19和CTX-M-27.采用ERIC-PER分析CTX-M-15产生株的同源性,39株大肠埃希菌被分为28个基因型,47株肺炎克雷伯菌被分为30个基因型.67.6%(25/37)和32.4%(12/37)bla_(CTX-M-15)分别位于65 000 bp和90 000 bp的可接合质粒上,65 000 bp质粒除bla_(CTX-M-15)阳性外,未检到bla_(TEM-1)、qnrB、bla_(DHA-1)、bla_(OXA-1),aac(6′)-I6-cr等耐药基因.1株接合菌90 000 bp质粒还存在bla_(OXA-1)和bla_(TEM-1)耐药基因,其余7个90 000 bp质粒所携耐药基因同65 000 bp质粒.所有bla_(CTX-M-15)都位于ISEcp1-like插入序列下游,ISEep1-like末端与blaCTX-M-15间距均为48 bp.结论 广州地区ESBLs主要分子表型为CTX-M型主要流行为CTX-M-14型.以CTX-M-15为代表能水解头孢他啶的CTX-M型ESBLs在本地区检出增多值得关注.     

Molecular characterization of extended-spectrum-β-lactamase-producing and plasmid-mediated AmpC β-lactamase-producing Escherichia coli isolated from stray dogs in South Korea

A total of 47 extended-spectrum-cephalosporin-resistant Escherichia coli strains isolated from stray dogs in 2006 and 2007 in the Republic of Korea were investigated using molecular methods. Extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase phenotypes were identified in 12 and 23 E. coli isolates, respectively. All 12 ESBL-producing isolates carried bla(CTX-M) genes. The most common CTX-M types were CTX-M-14 (n = 5) and CTX-M-24 (n = 3). Isolates producing CTX-M-3, CTX-M-55, CTX-M-27, and CTX-M-65 were also identified. Twenty-one of 23 AmpC β-lactamase-producing isolates were found to carry bla(CMY-2) genes. TEM-1 was associated with CTX-M and CMY-2 β-lactamases in 4 and 15 isolates, respectively. In addition to bla(TEM-1), two isolates carried bla(DHA-1), and one of them cocarried bla(CMY-2). Both CTX-M and CMY-2 genes were located on large (40 to 170 kb) conjugative plasmids that contained the insertion sequence ISEcp1 upstream of the bla genes. Only in the case of CTX-M genes was there an IS903 sequence downstream of the gene. The spread of ESBLs and AmpC β-lactamases occurred via both horizontal gene transfer, accounting for much of the CTX-M gene dissemination, and clonal spread, accounting for CMY-2 gene dissemination. The horizontal dissemination of bla(CTX-M) and bla(CMY-2) genes was mediated by IncF and IncI1-Iγ plasmids, respectively. The clonal spread of bla(CMY-2) was driven mainly by E. coli strains of virulent phylogroup D lineage ST648. To our knowledge, this is the first report of bla(DHA-1) in E. coli strains isolated from companion animals. This study also represents the first report of CMY-2 β-lactamase-producing E. coli isolates from dogs in the Republic of Korea.     

DNA sequence analysis of the genetic environment of various blaCTX-M genes

OBJECTIVES: Over a 3 year period (2000-2003) 21 Escherichia coli, 5 Klebsiella pneumoniae, 1 Serratia marcescens and 1 Proteus mirabilis producing CTX-M-type beta-lactamase were collected from five different hospitals in Paris, France. This study was conducted to analyse the genetic environment of these 28 bla(CTX-M) genes. METHODS: Antimicrobial susceptibility testing was performed by the disc diffusion method and MICs of various beta-lactams were determined by an agar dilution method. PCR was used to detect and sequence alleles encoding CTX-M, TEM, SHV and CMY enzymes. The genetic environment was analysed by amplification and direct sequencing using various set of PCR primers or cloning in pBK-CMV. RESULTS: Sequence analysis revealed that these isolates contained seven different bla(CTX-M) genes: bla(CTX-M-1) (4 strains), bla(CTX-M-2) (2 strains), bla(CTX-M-3) (4 strains), bla(CTX-M-9) (1 strain), bla(CTX-M-14) (5 strains), bla(CTX-M-15) (11 strains), bla(CTX-M-24) (1 strain). TEM-1 was associated with CTX-M-type enzymes in 15 isolates. Two strains produced both CTX-M-15 and SHV-2 or CTX-M-14 and CMY-2. In 25 strains the insertion sequence ISEcp1 was located upstream of the 5' end of the bla(CTX-M) gene. Among these strains, in five isolates, ISEcp1 was disrupted by insertion sequences such as IS26 (in three of them) or IS1 or IS10. Insertion sequence IS903 was found downstream of bla(CTX-M-14) or bla(CTX-M-24). Examination of the other three bla(CTX-M) genes (two bla(CTX-M-2) and one bla(CTX-M-9)) by cloning, sequencing and PCR analysis revealed the presence of complex Class 1 integrons, In35, an integron similar to In60 and a novel integron. CONCLUSIONS: This work further confirmed the predominant role of ISEcp1 in the mobilization of bla(CTX-M) genes of the CTX-M-1 cluster and the presence of In35, of an integron similar to In60 and a novel complex Class 1 integron.     

Dissemination of CTX-M-type beta-lactamases among clinical isolates of Enterobacteriaceae in Paris, France

We analyzed 19 clinical isolates of the family Enterobacteriaceae (16 Escherichia coli isolates and 3 Klebsiella pneumoniae isolates) collected from four different hospitals in Paris, France, from 2000 to 2002. These strains had a particular extended-spectrum cephalosporin resistance profile characterized by a higher level of resistance to cefotaxime and aztreonam than to ceftazidime. The bla(CTX-M) genes encoding these beta-lactamases were involved in this resistance, with a predominance of bla(CTX-M-15). Ten of the 19 isolates produced both TEM-1- and CTX-M-type enzymes. One strain (E. coli TN13) expressed CMY-2, TEM-1, and CTX-M-14. bla(CTX-M) genes were found on large plasmids. In 15 cases the same insertion sequence, ISEcp1, was located upstream of the 5' end of the bla(CTX-M) gene. In one case we identified an insertion sequence designated IS26. Examination of the other three bla(CTX-M) genes by cloning, sequencing, and PCR analysis revealed the presence of a complex sul1-type integron that includes open reading frame ORF513, which carries the bla gene and the surrounding DNA. Five isolates had the same plasmid DNA fingerprint, suggesting clonal dissemination of CTX-M-15-producing strains in the Paris area.     

Insertion sequence ISEcp1B is involved in expression and mobilization of a bla(CTX-M) beta-lactamase gene

The genetic structures (ca. 10-kb DNA fragment) surrounding the plasmid-borne extended-spectrum beta-lactamase bla(CTX-M-19) gene in a Klebsiella pneumoniae clinical isolate were determined. This beta-lactamase gene was part of a 4,797-bp transposon inserted inside orf1 of Tn1721. Inside this transposon, bla(CTX-M-19) was bracketed upstream and downstream by insertion sequences ISE cp1B and IS903D, respectively, and further downstream by a truncated gene encoding an outer membrane protein for iron transport. The single-copy ISEcp1B element was probably involved alone in the mobilization process that led to a 5-bp duplication at the target site of the transposed fragment. This mobilization event probably involved one inverted repeat of ISE cp1B and a second sequence farther away, resembling its second inverted repeat. Additionally, ISEcp1B provided -35 and -10 promoter sequences, contributing to the high-level expression of the bla(CTX-M-19) gene. Southern blot analysis failed to identify a reservoir of ISEcp1-like sequences among a series of gram-negative and gram-positive bacterial species usually found in the skin and intestinal human floras. The ability of ISEcp1-like elements to mobilize and to promote the expression of beta-lactamase genes may explain, in part, the current spread of CTX-M-type enzymes worldwide.     

产超广谱β-内酰胺酶表型及基因型特征的研究

目的分析大肠埃希菌、肺炎克雷伯菌临床分离株中超广谱β内酰胺酶（ESBL）的基因型分布情况。方法用表型确证试验确定临床标本中产ESBL的大肠埃希菌和肺炎克雷伯菌分别用TEM、SHV和CTX-M通用引物进行聚合酶链反应（PCR）扩增,鉴定其基因型。结果 66%的菌株为TEM基因型,14%的菌株为SHV基因型,10%的菌株为CTX-M型。结论大肠埃希菌、肺炎克雷伯菌临床分离株中超广谱β内酰胺酶（ESBL）的基因型分布以TEM基因型为主,部分菌株为SHV、CTX-M型。同一菌株内可以产生2种不同基因型的超广谱β-内酰胺酶。