大肠埃希菌与克雷伯菌属细菌qnr基因的检测

目的了解我院临床分离大肠埃希菌和克雷伯菌属细菌qnr基因的存在情况。方法用聚合酶链反应(PCR)对227株大肠埃希菌和36株克雷伯菌属细菌进行qnr基因检测。药敏检测分别采用K—B法、breakpoint法。结果227株大肠埃希菌和36株克雷伯菌属细菌中有6株细菌检出qnr基因(2株大肠埃希菌、1株产酸克雷伯菌、3株肺炎克雷伯菌)。其中产酸克雷伯菌为突变株,已在基因库注册,授权号：AY675584。6株qnr基因阳性菌株均为产超广谱β-内酰胺酶(ESBLs)且多重耐药菌株。结论qnr基因阳性菌株有严重的多重耐药性,我院克雷伯菌属细菌中qnr基因的携带率高于大肠埃希菌。     

质粒介导的大肠埃希菌和肺炎克雷伯菌耐喹诺酮类药物的研究

目的研究质粒介导的大肠埃希菌和肺炎克雷伯菌的流行情况及其对喹诺酮类药物耐药的作用。方法采用聚合酶链反应(PCR)对大肠埃希菌和肺炎克雷伯菌的qnr基因进行筛选,用实验证明qnr基因可以通过质粒介导并在细菌之间传递。结果在145株大肠埃希菌和125株肺炎克雷伯菌中共检出16株细菌携带qnr基因,其中12株为大肠埃希菌,4株肺炎克雷伯菌。16株qnr基因阳性菌株均为产超广谱内酰胺酶(ESBLs)菌株且呈多重耐药性。结论共检出16株细菌携带qnr基因,其阳性率为5.9%,大肠埃希菌阳性率高于肺炎克雷伯菌。qnr基因可以通过质粒介导,从供体菌接合转移至受体菌,且qnr在接合子中较稳定。     

基因qnr与大肠埃希菌和肺炎克雷伯菌耐药水平的相关性研究

目的 研究耐药基因qnr(qnrA,qnrB和qnrS)在大肠埃希菌和肺炎克雷伯菌环丙沙星敏感株与耐药株中与ESBLs阳性株和阴性株中的分布状况和比较分析.方法 从2006年全国美平耐药监测网点中收集241株非重复的大肠埃希菌(122株)和肺炎克雷伯菌(119株),用琼脂对倍稀释法测定所有菌株对药物环丙沙星、头孢他啶、头孢他啶/克拉维酸、头孢噻肟、头孢噻肟/克拉维酸的MIC值.采用PCR检测所有菌株的质粒介导喹诺酮耐药基因qnr.结果 在241椿筛选出的大肠埃希菌和肺炎克雷伯菌中,环丙沙星的敏感率为36.9%,耐药率为61.4%.头孢噻肟的敏感率为45.2%,耐药率为39.0%.头孢他啶的敏感率为74.3%.耐药率为19.9%.ESBLs阳性株占56.8%.qnr共检出46株,总阳性率为19.1%(46/241).其中qnrA有2株(0.8%,2/241),qnrB有25株(10.4%,25/241),qnrS有19株(7.9%,19/241).一株从痰标本分离的肺炎克雷伯菌同时检出qnrB和qnrS.在肺炎克雷伯菌中,qnr共检出39株,阳性率为32.8%(39/119);在大肠埃希菌中,qnr共检出6株,阳性率为4.9%(6/122).在环丙沙星敏感菌株中,qnr基因的阳性率为13.5%(12/89);在环丙沙星耐药菌株中,qnr基因的阳性率为21.6%(32/148).经X2检验,qnr基因在环丙沙星敏感菌株与耐药菌株检出率的差异无统计学意义(X2=2.435,P＞0.05).在ESBLs阳性的菌株中,qnr的阳性率为23.4%(32/137);在ESBLs阴性菌株中,qnr的阳性率为12.5%(13/104).经X2检验,qnr基因在ESBLs阳性株与ESBLs阴性株中检出率的差异具有统计学意义(X2=4.590,P＜0.05).结论 质柱介导喹诺酮类耐药基因qnr在大肠埃希菌和肺炎克雷伯菌中分布广泛.qnr基因与环丙沙星的耐药水平没有相关性,而与细菌是否产ESBLs有相关性.     

质粒介导的喹诺酮耐药qnr基因的检测

目的了解我院分离的革兰阴性杆菌中qnr基因的流行情况。方法PCR法对129株大肠埃希菌、29株肺炎克雷伯菌和10株阴沟肠杆菌进行qnr基因检测。对qnr基因阳性株,Ⅰ类整合酶基因扩增检测Ⅰ类整合子;KB纸片法检测对16种抗菌药的体外抗菌活性。按NCCLS表型筛选和确证试验检测产ESBLs株;琼脂稀释法检测对环丙沙星的MIC值。结果6株细菌检出qnr基因(5株大肠埃希菌和1株阴沟肠杆菌),肺炎克雷伯菌中未检出qnr基因。6株qnr基因阳性株Ⅰ类整合酶基因扩增全为阳性,仅对亚胺培南全部敏感且对多种抗菌药耐药,有2株大肠埃希菌对环丙沙星敏感。结论湖北地区存在qnr基因的流行,qnr基因阳性株多重耐药严重,应加强监控。     

产超广谱β-内酰胺酶肺炎克雷伯菌与大肠埃希菌qnrB基因的检测

目的:了解临床分离的产超广谱β-内酰胺酶(ESBLs)肺炎克雷伯菌和大肠埃希菌株qnrB基因的存在情况及与细菌耐药的关系。方法:收集福建省福州市三家"三甲"医院临床分离的菌株,菌株药敏试验检测采用K-B法,聚合酶链反应对42株产ESBLs肺炎克雷伯菌和44株产ESBLs大肠埃希菌进行qnrB基因筛查。结果:42株产ESBLs肺炎克雷伯菌有5株检出qnrB基因,检出率为11.90%,44株产ESBLs大肠埃希菌中有7株检出qnrB基因,检出率为15.91%。检出qnrB基因的5株肺炎克雷伯菌和7株大肠埃希菌对两种喹诺酮药物均耐药。结论:在福州地区产ESBLs的肺炎克雷伯菌和大肠埃希菌中存在qnrB基因,携带qnrB基因的12株细菌对左氟沙星和环丙沙星均耐药。     

对头孢吡肟敏感的疑似产超广谱β内酰胺酶大肠埃希菌和克雷伯菌属的分子生物学特征

目的 了解初筛试验疑似产超广谱β内酰胺酶(ESBLs)但确证试验未能确认,而对头孢吡肟敏感的大肠埃希菌和克雷伯菌属中的ESBLs和质粒介导的AmpC酶.方法 纸片扩散法检测18株细菌对常用抗菌药物的敏感性;PCR及多重PCR法检测细菌中的ESBLs和质粒AmpC酶基因;质粒转移接合试验检测耐药质粒的可传递性;细菌基因间重复一致序列(ERIC)-PCR法检测供体大肠埃希菌和受体E.coli J53及其接合子的同源性;脉冲场凝胶电泳(PFGE)对11株大肠埃希菌和6株肺炎克雷伯菌进行同源性分析.结果 18株细菌均为2005年1月至12月期间上海华山医院临床分离的菌株,其中大肠埃希菌11株,肺炎克雷伯菌6株,产酸克雷伯菌1株,按常规方法对细菌进行重新鉴定和药敏试验.18株细菌经美国临床和实验室标准协会(CLSI)推荐的ESBLs初筛试验结果均为ESBLs产生可疑菌株,但确证试验未能确认;所有菌株的头孢吡肟抑菌圈直径均在18 mm以上,显示敏感.PCR检测结果显示,11株大肠埃希菌中有9株产CIT型质粒AmpC酶,DNA测序及序列比对结果证实为CMY-2型AmpC酶,未发现TEM、SHV、CTX-M、PER、VEB、SFO等广谱或ESBLs;6株肺炎克雷伯菌中有5株产DHA型质粒AmpC酶,DNA测序及序列比对结果证实为DHA-1型AmpC酶;5株产DHA-1型AmpC酶的肺炎克雷伯菌株中,4株同时伴有广谱或ESBLs:其中2株产SHV-11型广谱酶,另2株分别产CTX-M-14型ESBLs和SHV-62型ESBLs;1株产酸克雷伯菌亦单产DHA-1型AmpC酶;质粒转移接合试验结果表明,携带耐药基因的质粒可从供体菌转移至敏感细胞中;PFGE结果显示,6株肺炎克雷伯菌的谱型各不相同,而11株大肠埃希菌可分为5种谱型,其中B型包含7株细菌,这7株细菌均产生质粒介导的CMY-2型AmpC酶,并分离自外科病房,提示可能存在克隆菌株的流行传播.结论在确证试验未能确认的疑似产ESBLs中,对头孢吡肟敏感的大肠埃希菌和克雷伯菌属细菌主要产生质粒介导的AmpC酶,但尚有少数菌株同时伴有产ESBLs.对同时产生ESBLs和AmpC酶的菌株,临床微生物实验室必须报告这些菌株对头孢吡肟耐药.     

2007年CHINET大肠埃希菌和克雷伯菌属耐药性监测

目的 了解2007年我国不同地区12所医院临床分离的大肠埃希菌和克雷伯菌属的耐药性.方法 采用纸片扩散法( K-B 法)对临床分离株作药敏试验.结果 共收集CHINET 细菌耐药性监测网12所医院分离的大肠埃希菌6 527株,肺炎克雷伯菌3 051株,催产克雷伯菌206株.其中儿童分离株大肠埃希菌和肺炎克雷伯菌分别占24.0%(1 566/6 527)和 17.8% (542/3 051).大肠埃希菌和克雷伯菌属产ESBLs菌株检出率分别平均为55.0%(12.3%~72.1%)和44.9%(15.4%~ 70.6% ).各医院ESBLs检出率存在一定差异.药敏结果显示,大肠埃希菌和克雷伯菌属对亚胺培南、美罗培南和头孢哌酮-舒巴坦都保持高度敏感,耐药率均低于10%.产ESBLs株对上述3种药物的耐药率也均低于20%.50%以上的产ESBLs株对庆大霉素和环丙沙星耐药.有5所医院分离出对碳青霉烯类抗生素不敏感菌株,其中肺炎克雷伯菌21株,大肠埃希菌2株,产酸克雷伯菌1株.其中20株肺炎克雷伯菌为泛耐药株,占0.7%(20/3 051).结论 大肠埃希菌和克雷伯菌属对碳青霉烯类抗生素和头孢哌酮-舒巴坦仍保持高度敏感性,不同地区的分离株中产ESBLs菌株检出率和药敏试验结果存在差异,儿童分离株中产ESBLs检出率上升值得关注.     

儿科临床分离株中质粒介导喹诺酮类药物耐药基因qnr在产ESBLs或AmpC酶大肠埃希菌和肺炎克雷伯菌中的流行

目的了解质粒介导喹诺酮类药物耐药基因qnr在儿科临床分离产ESBLs或AmpC酶大肠埃希菌和肺炎克雷伯菌中的流行情况与分布特点。方法琼脂稀释法测定抗生素MIC;PCR检测喹诺酮类药物耐药基因qnrA、qnrB和qnrS及相应ESBLs和AmpC酶基因;接合试验检测qnr基因是否可通过质粒转移;肠杆菌基因间重复一致序列-聚合酶链反应（ERIC—PCR）检测qnr阳性菌株的同源性。结果702株儿科临床分离产ESBLs或AmpC酶大肠埃希菌和肺炎克雷伯菌共检出含qnr基因菌株99株（14．1％）,其中qnrA、qnrB和qnrS的检出率分别为1．1％（8株）、4．0％（28株）和9．5％（67株）,其中3株菌同时含有qnrA和qnrB,1株含qnrB和qnrS。在99株qnr阳性菌株中,有88株（88．9％）检测到至少1种bla基因。20株qnr阳性菌株通过接合试验传递成功。相对于受体菌,接合子对环丙沙星的MIC提高了2～125倍。ERIC—PCR显示99株qnr阳性菌株有不同的DNA条带,提示其可能属于不同的克隆株。结论在702株儿科临床分离产ESBLs或AmpC酶大肠埃希菌和肺炎克雷伯菌中,质粒介导喹诺酮类药物耐药基因qnr携带率为（14．1％）,qnrS为最流行的亚型。88．9％的qnr阳性株携带1种或1种以上bla基因。     

大肠埃希菌耐药特征及质粒介导喹诺酮耐药基因分布北大核心CSCD

目的调查大肠埃希菌分离株的耐药特征及质粒介导喹诺酮耐药基因流行状况。方法纸片扩散（K-B）法进行药物敏感试验,采用双纸片法检测产超广谱β内酰胺酶（ESBL）,聚合酶链反应（PCR）检测qnr A、qnr B、qnr C、qnr D、qnr S、aac（6＇）-Ib、qep A基因,限制性酶切反应确定aac（6＇）-Ib-cr基因型。结果 179株大肠埃希菌中95株ESBL表型确证试验阳性,检出率为53.1%;产ESBL菌株未见对美罗培南耐药,对亚胺培南耐药率极低（1.1%）,对阿米卡星、哌拉西林-他唑巴坦、头孢哌酮-舒巴坦耐药率皆低于30%,对哌拉西林、头孢噻肟、头孢曲松、氨曲南、甲氧苄啶-磺胺甲唑耐药率皆高于70%,对庆大霉素、头孢他啶、环丙沙星、左氧氟沙星耐药率在60%~70%;PCR扩增结果显示产ESBL菌株,具有qnr基因9株（9.5%）,其中qnr A 2株、qnr B 5株、qnr S 2株。非产ESBL菌株,具有qnr B基因3株（3.6%）;酶切反应显示产和非产ESBL菌株具有aac（6＇）-Ib-cr基因分别为21株（22.1%）和5株（6.0%）。所有菌株皆未检测到qep A基因。结论产ESBL大肠埃希菌呈现多重耐药趋势,质粒介导喹诺酮耐药基因以aac（6＇）-Ib-cr基因型为主。     

大肠埃希菌耐药特征及质粒介导喹诺酮耐药基因分布

目的调查大肠埃希菌分离株的耐药特征及质粒介导喹诺酮耐药基因流行状况。方法纸片扩散(K-B)法进行药物敏感试验,采用双纸片法检测产超广谱β内酰胺酶(ESBL),聚合酶链反应(PCR)检测qnr A、qnr B、qnr C、qnr D、qnr S、aac(6')-Ib、qep A基因,限制性酶切反应确定aac(6')-Ib-cr基因型。结果 179株大肠埃希菌中95株ESBL表型确证试验阳性,检出率为53.1%;产ESBL菌株未见对美罗培南耐药,对亚胺培南耐药率极低(1.1%),对阿米卡星、哌拉西林-他唑巴坦、头孢哌酮-舒巴坦耐药率皆低于30%,对哌拉西林、头孢噻肟、头孢曲松、氨曲南、甲氧苄啶-磺胺甲唑耐药率皆高于70%,对庆大霉素、头孢他啶、环丙沙星、左氧氟沙星耐药率在60%~70%;PCR扩增结果显示产ESBL菌株,具有qnr基因9株(9.5%),其中qnr A 2株、qnr B 5株、qnr S 2株。非产ESBL菌株,具有qnr B基因3株(3.6%);酶切反应显示产和非产ESBL菌株具有aac(6')-Ib-cr基因分别为21株(22.1%)和5株(6.0%)。所有菌株皆未检测到qep A基因。结论产ESBL大肠埃希菌呈现多重耐药趋势,质粒介导喹诺酮耐药基因以aac(6')-Ib-cr基因型为主。     

Emerging plasmid-mediated quinolone resistance associated with the qnr gene in Klebsiella pneumoniae clinical isolates in the United States

Although quinolone resistance commonly results from chromosomal mutation, recent studies indicate that such resistance can also be transferred on plasmids carrying the gene responsible, qnr. One hundred ten ciprofloxacin-resistant clinical isolates of Klebsiella pneumoniae and Escherichia coli from the United States were screened for the qnr gene by PCR and Southern hybridization of plasmid DNA. Conjugation experiments were done with azide-resistant E. coli J53 as the recipient and selection with azide and sulfonamide, a resistance frequently linked to qnr. EcoRI and BamHI digests of qnr-hybridizing plasmids were subjected to electrophoresis on agarose gels and probed with qnr by Southern hybridization. qnr was detected in 8 (11.1%) of 72 K. pneumoniae strains. These eight positive strains were from six states in the United States. qnr was not found in any of the 38 E. coli strains tested. Quinolone resistance was transferred from seven of the eight probe-positive strains. Transconjugants with qnr-hybridizing plasmids had 32-fold increases in ciprofloxacin MICs relative to E. coli J53. For all eight strains, the sequence of qnr was identical to that originally reported. By size and restriction digests, four plasmids were related to the first-reported plasmid, pMG252, and three were different. Five new qnr plasmids encoded FOX-5 beta-lactamase, as did pMG252, but two others produced SHV-7 extended-spectrum beta-lactamase. Transferable plasmid-mediated quinolone resistance associated with qnr is now widely distributed in quinolone-resistant clinical strains of K. pneumoniae in the United States. Plasmid-determined quinolone resistance contributes to the increasing quinolone resistance of K. pneumoniae isolates and to the linkage previously observed between resistance to quinolones and the latest beta-lactam antibiotics.     

Detection of the plasmid-mediated quinolone resistance determinant qnr among clinical isolates of Klebsiella pneumoniae producing AmpC-type beta-lactamase

OBJECTIVES: Plasmid pMG252 contains the qnr locus, which is responsible for low-level resistance to quinolones by protecting the DNA gyrase. pMG252 also encodes the AmpC-type beta-lactamase (pACBL), FOX-5. The aim of this study was to determine the prevalence of qnr in strains from different geographical locations in America and Europe. METHODS: Four hundred and twenty-five (159 Klebsiella pneumoniae and 266 Escherichia coli) clinical isolates were studied. The detection of qnr was by PCR using specific primers for an internal fragment of 543 bp. RESULTS: qnr was detected in three cefoxitin-resistant K. pneumoniae strains, which also produced a pACBL. None of the E. coli isolates tested contained qnr. The three qnr-positive K. pneumoniae came from the USA, and all transferred a conjugative plasmid coding for cefoxitin resistance to E. coli J53. qnr was also transferred by the same plasmid in two out of the three strains. The sequences of amplified qnr fragments from the three strains were identical to the qnr sequence from pMG252. CONCLUSIONS: The qnr determinant is uncommon among clinical isolates of K. pneumoniae and E. coli, but its identification in three pACBL+ K. pneumoniae from the USA indicates the emergence of this quinolone resistance mechanism.     

Epidemiology of conjugative plasmid-mediated AmpC beta-lactamases in the United States

A sample of 752 resistant Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli strains from 70 sites in 25 U.S. states and the District of Columbia was examined for transmissibility of resistance to ceftazidime and the nature of the plasmid-mediated beta-lactamase involved. Fifty-nine percent of the K. pneumoniae, 24% of the K. oxytoca, and 44% of the E. coli isolates transferred resistance to ceftazidime. Plasmids encoding AmpC-type beta-lactamase were found in 8.5% of the K. pneumoniae samples, 6.9% of the K. oxytoca samples, and 4% of the E. coli samples, at 20 of the 70 sites and in 10 of the 25 states. ACT-1 beta-lactamase was found at eight sites, four of which were near New York City, where the ACT-1 enzyme was first discovered; ACT-1 beta-lactamase was also found in Massachusetts, Pennsylvania, and Virginia. FOX-5 beta-lactamase was also found at eight sites, mainly in southeastern states but also in New York. Two E. coli strains produced CMY-2, and one K. pneumoniae strain produced DHA-1 beta-lactamase. Pulsed-field gel electrophoresis and plasmid analysis suggested that AmpC-mediated resistance spread both by strain and plasmid dissemination. All AmpC beta-lactamase-containing isolates were resistant to cefoxitin, but so were 11% of strains containing transmissible SHV- and TEM-type extended-spectrum beta-lactamases. A beta-lactamase inhibitor test was helpful in distinguishing the two types of resistance but was not definitive since 24% of clinical isolates producing AmpC beta-lactamase had a positive response to clavulanic acid. Coexistence of AmpC and extended-spectrum beta-lactamases was the main reason for these discrepancies. Plasmid-mediated AmpC-type enzymes are thus responsible for an appreciable fraction of resistance in clinical isolates of Klebsiella spp. and E. coli, are disseminated around the United States, and are not so easily distinguished from other enzymes that mediate resistance to oxyimino-beta-lactams.     

Plasmid-mediated quinolone resistance in clinical isolates of Escherichia coli from Shanghai,China

Although quinolone resistance usually results from chromosomal mutations, recent studies indicate that quinolone resistance can also be plasmid mediated. The gene responsible, qnr, is distinct from the known quinolone resistance genes and in previous studies seemed to be restricted to Klebsiella pneumoniae and Escherichia coli isolates from the University of Alabama in Birmingham, where this resistance was discovered. In Shanghai, the frequency of ciprofloxacin resistance in E. coli has exceeded 50% since 1993. Seventy-eight unique ciprofloxacin-resistant clinical isolates of E. coli from Shanghai hospitals were screened for the qnr gene by colony blotting and Southern hybridization of plasmid DNA. Conjugation experiments were done with azide-resistant E. coli J53 as a recipient with selection for plasmid-encoded antimicrobial resistance (chloramphenicol, gentamicin, or tetracycline) and azide counterselection. qnr genes were sequenced, and the structure of the plasmid DNA adjacent to qnr was analyzed by primer walking with a sequential series of outward-facing sequencing primers with plasmid DNA templates purified from transconjugants. Six (7.7%) of 78 strains gave a reproducible hybridization signal with a qnr gene probe on colony blots and yielded strong signals on plasmid DNA preparations. Quinolone resistance was transferred from all six probe-positive strains. Transconjugants had 16- to 250-fold increases in the MICs of ciprofloxacin relative to that of the recipient. All six strains contained qnr with a nucleotide sequence identical to that originally reported, except for a single nucleotide change (CTA-->CTG at position 537) encoding the same amino acid. qnr was located in complex In4 family class 1 integrons. Two completely sequenced integrons were designated In36 and In37. Transferable plasmid-mediated quinolone resistance associated with qnr is thus prevalent in quinolone-resistant clinical strains of E. coli from Shanghai and may contribute to the rapid increase in bacterial resistance to quinolones in China.     

Antibiotic prescribing in general practice: striking differences between Italy (Ravenna) and Denmark (Funen)

The aim of this study was to evaluate the incidence of decreased susceptibility to broad-spectrum cephalosporins in Enterobacteriaceae that lack inducible chromosomal bla genes, and to determine the enzymes responsible for resistance. From all clinically relevant Enterobacteriaceae strains isolated between 1994 and 1996, 88 of 7054 Escherichia coli, seven of 581 Klebsiella pneumoniae and 23 of 166 Klebsiella oxytoca strains were studied because of their decreased susceptibilities to broad-spectrum cephalosporins (as reflected in intermediate susceptibilities and/or positive synergy tests and/or irregular crenellated inhibition zones). The most frequent mechanism implicated in decreased susceptibility to broad-spectrum cephalosporins displayed by E. coli and K. oxytoca was hyperproduction of chromosomal beta-lactamase, followed by plasmid-mediated SHV-1 hyperproduction in E. coli. In our hospital, the incidence of plasmid-mediated extended-spectrum beta-lactamases (ESBLs) between 1994 and 1996 was low. ESBLs were found in only 10 (0.14%) E. coli strains (six CTX-M-9, two TEM-12 and two SHV-2), in one (0.17%) K. pneumoniae strain (SHV-2) and in no K. oxytoca strains. The relatively wide variety of beta-lactamases that were detected among these common bacteria isolated from a single medical centre, including non-TEM- and non-SHV-derived ESBLs, appears epidemiologically remarkable.     

Mutants of the TEM-1 beta-lactamase conferring resistance to ceftazidime

Spontaneous ceftazidime resistant mutants were obtained from an Escherichia coli K12 J62-2 expressing the TEM-1 beta-lactamase (mutation frequency = 10(-9). These mutants produced beta-lactamases with similar molecular weights, kinetic parameters and isoelectric points (pI) to the beta-lactamases produced by ceftazidime resistant clinical isolates which have recently been identified in this laboratory. Mutant enzyme A focused as a doublet band at pI 5.3 with an additional weak pI 5.4 band. The doublet co-focused with the TEM-E2 beta-lactamase, produced by a ceftazidime resistant Klebsiella oxytoca isolate, which was originally obtained in a Liverpool hospital. Mutant enzyme B had a pI identical to the TEM-E1 beta-lactamase produced by a ceftazidime resistant clinical isolate of E. coli found in Belgium. These results suggest that the two beta-lactamases in the clinical strains may have come from simple mutations of the TEM-1 beta-lactamase gene.     

qnrA in CTX-M-producing Escherichia coli isolates from France

By PCR, we screened for qnr genes 112 clinical isolates of extended-spectrum beta-lactamase-producing Escherichia coli collected from hospitals in France during 2004. For the first time, 7.7% of CTX-M-producing E. coli isolates presented a plasmid-mediated resistance to quinolones. All strains harbored a qnrA gene located on a sul1-type class 1 integron with similar structure to the In36 integron.     

AcrAB Efflux System: Expression and Contribution to Fluoroquinolone Resistance in Klebsiella spp

Seven Klebsiella pneumoniae and four Klebsiella oxytoca clinical isolates with different levels of resistance to ciprofloxacin were studied. Mutations in the topoisomerase genes were found in almost all strains, but the contribution of a multidrug efflux system homologous to AcrAB in Escherichia coli was also observed. Overexpression of this efflux system was demonstrated by immunoblotting with antibodies against E. coli AcrA.     

Regional variation in the prevalence of extended-spectrum beta-lactamase-producing clinical isolates in the Asia-Pacific region (SENTRY 1998-2002)

We examined the prevalence of extended-spectrum beta-lactamase (ESBL)-producing strains of Klebsiella pneumoniae, Klebsiella oxytoca, Escherichia coli, Proteus mirabilis, Citrobacter koseri, and Salmonella spp. that were isolated as part of the SENTRY Asia-Pacific Surveillance Program between 1998 and 2002. During the study period, a total of 6,388 strains were gathered from 17 medical centers in 7 countries and examined for ESBL production and hyperproduction of K. oxytoca chromosomal K1 beta-lactamase enzyme. High rates of confirmed ESBL-producing isolates were found in K. pneumoniae strains from Singapore (35.6%), followed by those from mainland China (30.7%), South Africa (28.1%), and the Philippines (21.9%), whereas the rates were less than 10% in Japan and Australia. ESBL-producing E. coli strains were also prominent in mainland China (24.5%), Hong Kong (14.3%), and Singapore (11.3%). ESBL-producing K. oxytoca were common in the Philippines (38.5%), Singapore (33.3%), and China (30.0%). Hyperproduction of K. oxytoca chromosomal K1 beta-lactamase enzyme was common in Australia and Japan. P. mirabilis strains from Singapore produced ESBL (17.9%) despite the low prevalence (0-8.1%) in other countries. Few ESBL-producing C. koseri and Salmonella spp. strains were found in Japan, Singapore, Taiwan, and South Africa. Although there was variation among countries in substrate preference, ceftazidime was more likely to detect presumptive ESBL phenotype in K. pneumoniae and aztreonam more likely in E. coli, whereas ceftriaxone was the best substrate for the confirmation of ESBL production. ESBL-producing strains showed high levels of co-resistance to aminoglycosides, tetracycline, trimethoprim-sulfamethoxazole, and ciprofloxacin. Imipenem retained activity against all ESBL-producing strains. Organisms expressing ESBLs are widely distributed in the Asia-Pacific region, although prevalence rates vary significantly.