多重耐药菌中质粒介导喹诺酮耐药基因的检测和分析

目的分析广州医学院第一附属医院临床分离的60株多重耐药大肠埃希菌和肺炎克雷伯菌质粒介导的喹诺酮耐药基因存在状况。方法采用VITEK-2全自动细菌鉴定仪检测大肠埃希菌和肺炎克雷伯菌对抗生素的药物敏感性,选择多重耐药的大肠埃希菌和肺炎克雷伯菌作为研究对象,用多重PCR法进行质粒介导的喹诺酮耐药基因的检测和分析。结果检测出耐药基因qnrA型2株,qnrB型耐药基因15株,aac（6’）-Ib基因9株,其中aac（6’）-Ib—cr型耐药基因5株。其中有1株肺炎克雷伯菌检测到同时含有qnrA和aac（6’）-Ib—cr基因;还有3株肺炎克雷伯菌检测到同时含有qnrB和aac（6’）-Ib—cr基因。未检测到qnrC、qnrD、qnrS、qepA型的耐药基因。结论临床分离的多重耐药大肠埃希菌和肺炎克雷伯菌含有多种质粒介导的喹诺酮耐药基因,应引起临床的重视。     

大肠埃希菌耐喹诺酮类抗菌药的相关耐药基因检测及耐药机制分析

目的 探讨大肠埃希菌耐喹诺酮类抗菌药的相关耐药基因检测及耐药机制.方法 选取我院尿液等排泄物和分泌物标本中分离出的150株大肠埃希菌株,应用纸片扩散法进行药敏试验,采用PCR技术检测qnr以及aac(6')-Ib-cr质粒基因的表达,并对PCR产物进行DNA测序分析.结果 150株大肠埃希菌对喹诺酮类抗菌药物的耐药率均超过50％,20株菌检出阳性基因qnrB,qnrS以及aac(6')-Ib-cr的阳性率分别为12.20％、9.76％、13.41％,共有8株菌同时携带超过2种质粒基因,其对喹诺酮类药物均耐药,同时合并有其他类型抗菌药物的耐药情况,12株菌检出单个质粒基因,其中4株对喹诺酮类敏感.结论 大肠埃希菌的耐药情况十分严重,存在qnrB、qnrS、aac(6')-1b-cr流行,并存在两种及多种耐药基因共存于同一细菌中的现象,质粒介导的喹诺酮耐药基因数量与耐药种类数量呈正相关.     

大肠埃希菌gyrA、parC和marOR基因突变与喹诺酮耐药的相关性

目的:研究大肠埃希菌gyrA、parC和marOR基因突变与喹诺酮类耐药的相关性。方法:采用微量稀释法进行常规药敏试验,筛选3株萘啶酸敏感大肠埃希菌和37株萘啶酸耐药大肠埃希菌株;PCR扩增大肠埃希菌喹诺酮耐药决定区(QRDR)相关gyrA、parC基因,进行聚合酶链反应-单链构象多态性(PCR-SSCP)分析,同时PCR扩增marOR基因;在耐药株选取部分菌株对gyrA、parC及marOR基因进行测序,检测其突变情况,其结果与体外药敏试验结果进行比较,研究其相关性。结果:37株耐药株均出现gyrA基因突变,但对环丙沙星低耐株最低抑菌浓度(MIC)=2mg/L只出现gyrA单位点突变,而parC基因未发生突变;环丙沙星高耐株(MIC=64mg/L)gyrA基因出现3个位点突变,parC基因出现单位点突变;在环丙沙星高耐株(MIC=256mg/L),并伴有其他类抗菌药物的多重耐药时,除了出现gyrA和parC基因双位点突变,同时检测到marOR基因的多位点突变。结论:gyrA和parC基因突变在大肠埃希菌对喹诺酮耐药中起着重要作用,gyrA和parC基因突变的程度与大肠埃希菌耐药水平有关,marOR基因多位点突变在多重耐药机制中具有一定的作用。     

大肠埃希菌中Ⅰ类整合子耐药基因的分析

目的 对临床分离大肠埃希菌株携带的Ⅰ类整合子及相关耐药基因进行筛选和分析.探讨Ⅰ类整合子在大肠埃希菌耐药中的作用.方法 对43株大肠埃希菌临床分离株做药敏试验;采用PCR扩增、DNA测序、DNA序列比对的方法 对其携带的Ⅰ类整合子相关耐约基因进行分析.结果 43株大肠埃希菌分离株对10种抗菌药物的耐药率依次为亚胺培南4.7%、阿米卡星18.6%、头孢他啶、27.9%、头孢吡肟37.2%、头孢呋辛55.8%、复方磺胺甲嗯唑58.1%、妥布霉素74.4%、庆大霉素79.1%、头孢噻肟81.4%和哌拉两林83.7%.在43株大肠埃希菌分离株中有25株含有Ⅰ类整合子,其中18株携带整合子相关耐药基因,如介导对磺胺类和氨基糖苷类约物的耐药基因等;某些菌株携带的整合子相关耐药基因相同.结论 Ⅰ类整合子在大肠埃希菌中广泛存在,整合子相关耐约基因在该菌耐药性的形成和播散中发挥作用.     

产超广谱β-内酰胺酶的肠杆菌科细菌对喹诺酮类药物的耐药性分析

目的　分析从临床老年患者分离的产 ESBL s肠杆菌科细菌对喹诺酮类药物的耐药性。方法　利用法国 Bio- Merieux公司生产的全自动细菌分析系统 VITEK- 6 0和革兰氏阴性杆菌鉴定卡 GNI 及药敏卡 GNS- 5 0 6、GNS- 12 0对老年患者各种标本分离得到的 12 70株肠杆菌科细菌进行喹诺酮类抗菌药物耐药试验及 ESBL s检测 ,ESBL s产酶率为 2 0 .6 %。分析其中 ESBL s阳性的 2 4 1株菌株对喹诺酮抗菌药物环丙沙星、左氧氟沙星、培氟沙星和萘啶酸的耐药特性。结果　产 ESBL s的大肠埃希氏菌对这四种抗菌药物均高度耐药 ,耐药率在 92 .4 %以上。同时 ,喹诺酮类药物对肺炎克雷伯氏菌的体外抗菌活性亦不高 :左氧氟沙星、环丙沙星耐药率为 6 1.8% ,培氟沙星、萘啶酸的耐药率超过 70 %。而其它产 ESBL s的肠杆菌科细菌对左氧氟沙星、环丙沙星有较高的敏感性 ,敏感率为 77.4 % ,但培氟沙星、萘啶酸的耐药程度较高 ,耐药率为 75 .0 %。结论　应避免使用喹诺酮抗菌药物治疗 ESBL s阳性的大肠埃希氏菌感染。对肺炎克雷伯氏菌的 ESBL s产酶株 ,喹诺酮抗菌药物有一定的体外抗菌活性 ,临床使用时应以体外药敏试验结果为依据谨慎使用。除大肠埃希氏菌、肺炎克雷伯氏菌以外的 ESBL s阳性肠杆菌科细菌的感染 ,左氧氟沙星、环丙沙星     

质粒介导的喹诺酮耐药基因在中国大陆尿液分离的大肠埃希菌中的广泛分布

目的分析中国大陆20家三甲医院尿来源大肠埃希菌的耐药特点并调查质粒介导的喹诺酮类耐药基因的分布情况和流行特点。方法收集卫生部全国耐药监测网2007年1月至2008年3月非重复298株尿液分离大肠埃希菌;琼脂稀释法测定其对20种抗菌药物的敏感性,多聚酶链反应和DNA测序分析qn-rA,qnrB,qnrS,aac(6’)-ib和qepA基因的流行性;接合实验分析质粒的转移性;Eric-PCR分析喹诺酮基因阳性菌株之间的遗传相关性;卡方检验用于分析耐药基因与氟喹诺酮耐药之间的相关性。结果 298株大肠埃希菌对20种抗菌药物耐药现象严重,其中对环丙沙星和左氧氟沙星有很高的耐药性,耐药率高达78.5%和74.2%。经基因比对分析,62株(20.8%)细菌携带aac(6’)-Ib基因;45株(15.1%)细菌携带喹诺酮耐药基因,1株(0.3%)检测出qnrA基因,3株(11.4%)检出qnrB基因,5株(1.7%)检出qnrS基因,25株(8.4%)确定为aac(6’)-Ib-cr基因,12株(4.7%)检出qepA基因;此外,有3株细菌分别发现aac(6’)-Ib-cr和qepA1基因aac(6’)-Ib-cr和qnrB1基因,qepA和qnrS1基因共存。45株喹诺酮基因阳性菌株之间具有很大的遗传差异,并且其中有16株细菌携带的基因具有可转移性。aac(6’)-Ib的流行性与细菌的环丙沙星和左氧氟沙星不敏感性相关(P<0.05);喹诺酮耐药基因的流行性与细菌的氟喹诺酮不敏感性相关(P<0.05)。结论尿液分离的大肠埃希菌耐药严重,质粒介导的喹诺酮耐药基因主要以aac(6’)-ib-cr为主,qepA1次之,这些潜在播散的喹诺酮耐药基因对于临床尿路感染的治疗有很大的挑战。     

大肠埃希菌临床分离株Ⅰ类整合子分布与耐药相关性研究

目的 川北地区大肠埃希菌的整合子携带情况及其与耐药性之间的关系.方法 采用琼脂稀释法测定临床分离的180株大肠埃希菌对15种抗菌药物的敏感性,敏感、中介、耐药采用美国临床实验室标准化协会(CSLI)2006年公布的标准判定.PCR方法检测临床大肠埃希菌中的第一类整合酶基因(intI),应用统计学方法比较第一类整合酶基因(intI)阳性与阴性菌株的耐药性差异,分析Ⅰ类整合子与耐药性形成的的相关性.结果 180株大肠埃希菌对氨苄西林、环丙沙星、左旋氧氟沙星、庆大霉素、复方磺胺甲嗯唑、头孢唑啉、妥布霉素、氨苄西林/舒巴坦、头孢曲松的耐药率高,达32.9%～92.3%.临床分离180株大肠埃希菌中intI带率为64.4%,intI性菌株对β-内酰胺类、喹诺酮类和氨基糖苷类等抗菌药物呈现多重耐药性.结论 川北地区大肠埃希菌对临床常用抗菌药物耐药突出.intI携带率高,并且与耐药性的形成关系密切.     

天津地区大肠埃希菌临床株质粒介导的喹诺酮类耐药机制的研究

目的 了解天津地区临床分离的大肠埃希菌中qnr,aac(6')-Ib-cr及gepA基因的流行情况,分析阳性菌株感染的微生物学及临床特征.方法 从天津某三甲医院收集环丙沙星耐药(CPLX,MIC 4gg/mL)的大肠埃希菌共75株,采用PCR法检测gnrA,gnrB,gnrS,aac(6')-Ib及gepA基因,对aac(6'),-Ib基因阳性菌株用Fok I酶切确认aac(6')-Ib-cr基因,接合试验验证qnr的转移性.所有阳性菌株用PCR法检测p-内酰胺酶基因,并收集阳性菌株感染患者临床资料进行分析.结果 75株环丙沙星耐药的大肠埃希菌中共有18株(24%)携带qnr基因和(或)aac(6)-Ib-cr基因,其中gnrB,gnrS和aac(6')-Ib-cr检出率分别为5.3%,4%和21.3%,未检出gnrA和gepA o 5株qnr阳性菌株均接合传递成功.18株gnr1aac(6')-1b-cr阳性的大肠埃希菌中均检测出R-内酸胺酶基因.阳性菌株对喹诺酮类和头孢菌素类药物高度耐药且主要来源于泌尿系感染,感染患者均为中老年人.结论 天津地区临床存在qnr和aac(6')-Ib-cr阳性菌株的流行,这是首次在天津发现qnr介导的喹诺酮类耐药.     

肝硬化腹腔感染抗生素应用的流行病学分析

对５６例肝硬化腹腔感染患者的感染菌分布及抗菌药物的应用等作流行病学分析。结果显示：腹腔感染的细菌种类以大肠埃希氏菌、肺炎克雷伯氏菌为多,占所分离菌株的６０．３％;腹腔感染与病死率有直接关系占５９．０９％。大肠埃希氏菌对诺氟沙星、环丙沙星、氧氟沙星耐药率分别为２８．５７％、２０％、１５．３８％。而肺炎克雷伯氏菌对氟喹诺酮类无耐药株。注射用头孢哌酮、头孢曲松、头孢噻肟、头孢唑肟基本无耐药株,临床最常用的头孢唑林已有耐药株,其中大肠埃希氏菌的耐药率为１０％,肺炎克雷伯氏菌为１６．６７％,提示临床医师合理应用抗菌药物在肝硬化腹腔感染治疗中具有重要意义。     

产超广谱β-内酰胺酶(ESBLs)大肠埃希菌对喹诺酮类药物的耐药性观察

目的探讨产超广谱β-内酰胺酶(ESBLs)大肠埃希菌对喹诺酮类药物的耐药情况。方法选择南阳市中心医院2008年9月至2010年9月从分类标本中分类的大肠埃希菌共200株,经超广谱β-内酰胺酶酶确证试验,其中105株产生ESBLs。观察105株超广谱β-内酰胺酶大肠埃希菌对环丙沙星、左氧沙星、莫西沙星的耐药情况。结果 200株大肠埃希菌中,产超广谱β-内酰胺酶酶菌株的检出率为52.5%;产超广谱β-内酰胺酶大肠埃希菌对左氧氟沙星的耐药率显著高于非超广谱β-内酰胺酶大肠埃希菌耐药率,差异有统计学意义(P<0.05);105株产超广谱β-内酰胺酶大肠埃希菌对喹诺酮类药物耐药的最低抑菌浓度检测结果,89.5%对环丙沙星最低抑菌浓度值>4μg/mL;87.6%对左氧氟沙星最低抑菌浓度值>8μg/mL,89.5%对莫西沙星最低抑菌浓度值>2μg/mL。尿标本产超广谱β-内酰胺酶大肠埃希菌均对3种喹诺酮类药物耐药,耐药率达82.9%;痰标本大肠埃希菌,耐药率为92.3%。结论产β-内酰胺酶大肠埃希菌所占检出大肠埃希菌中的比例较大,且对喹诺酮类药物耐药率高,临床应用中要调整喹诺酮类使用频率,减少耐药菌株出现。     

Characterization of antimicrobial resistance patterns and class 1 integrons in Escherichia coli O26 isolated from humans and animals

Antimicrobial resistance patterns and the prevalence of antimicrobial resistance genes and class 1 integrons in 35 Escherichia coli O26 isolated from humans and food-producing animals were evaluated. All isolates were resistant to cefaclor, cefalothin and sulfonamide and were susceptible to amikacin, gentamicin, cefmetazole, cefotaxime, ceftriaxone, ciprofloxacin, norfloxacin and trimethoprim. Most isolates were resistant to aztreonam, ampicillin, tetracycline, streptomycin and kanamycin. All ampicillin- and streptomycin-resistant E. coli O26 carried ampC and strA-strB gene sequences, respectively. Florfenicol- and chloramphenicol-resistant isolates carried floR but not cmlA. Class1 integrons were identified in 14% of E. coli O26 isolates. To our knowledge, this is the first report describing the presence of multiple antimicrobial resistance genes in E. coli O26 isolated from human and animal origins.     

High prevalence of plasmid-mediated quinolone resistance determinant aac(6')-Ib-cr amongst Salmonella enterica serotype Typhimurium isolates from hospitalised paediatric patients with diarrhoea in China

In this study, the antimicrobial susceptibilities and prevalence of plasmid-mediated quinolone resistance determinants amongst Salmonella enterica serotype Typhimurium isolates from hospitalised paediatric patients with diarrhoea in China were investigated. In total, 40 (64.5%) of 62 S. Typhimurium isolates were resistant to ciprofloxacin (minimum inhibitory concentration ≥0.5 μg/mL), comprising 28 isolates with low-level resistance and 12 isolates with high-level resistance. All ciprofloxacin-resistant isolates were multiresistant to other antimicrobial agents. Four pulsed-field gel electrophoresis (PFGE) clusters were found amongst the 40 ciprofloxacin-resistant isolates, amongst which PFGE clusters A, B, E and D accounted for 7, 4, 1 and 28 isolates, respectively. Two isolates with high-level ciprofloxacin resistance had two mutations in the quinolone resistance-determining regions (QRDRs) of gyrA and parC. The remaining ciprofloxacin-resistant isolates had only one mutation in the QRDR of gyrA. All 62 S. Typhimurium isolates were negative for qnr genes and qepA and 23 (37.1%) of the isolates were positive for aac(6')-Ib-cr. Nineteen isolates harbouring aac(6')-Ib-cr belonged to PFGE cluster D. A high prevalence of ciprofloxacin resistance and aac(6')-Ib-cr was found amongst S. Typhimurium isolates in China from hospitalised paediatric patients with diarrhoea not receiving quinolones. A single mutation in the QRDR of gyrA as well as production of AAC(6')-Ib-cr contributed to ciprofloxacin resistance. Clonal spread was responsible for the dissemination of aac(6')-Ib-cr amongst S. Typhimurium isolates.     

1999-2003年广东和辽宁地区大肠埃希菌和肺炎克雷伯菌临床分离株耐药性比较分析

目的调查1999-2003年国家细菌耐药性监测网广东和辽宁地区大肠埃希菌和肺炎克雷伯菌临床分离株的耐药性,比较不同来源菌株之间耐药率的差别。方法药物敏感性试验采用纸片扩散法,用WHONET5软件进行结果分析。结果 5年间共收集大肠埃希菌6 816株和肺炎克雷伯菌4 411株。尿液、痰和血液等是大肠埃希菌和肺炎克雷伯菌临床分离株的主要标本来源。1999-2003年广东和辽宁地区大肠埃希菌临床分离株对亚胺培南最为敏感,其次为阿米卡星和头孢他啶。大肠埃希菌临床分离株,广东地区的菌株对头孢噻肟的耐药率最高,2003 年增加到32．0％,两地区分离的大肠埃希菌对环丙沙星的耐药率高于60%。肺炎克雷伯菌临床分离株对亚胺培南最为敏感,其次为头孢吡肟、头孢他啶、阿米卡星和环丙沙星。在1999-2003年间,广东和辽宁地区的肺炎克雷伯菌临床分离株对头孢噻肟和头孢他啶的耐药率逐年增高,环丙沙星的耐药率也有一定程度的增高。广东和辽宁地区产超广谱β内酰胺酶(ESBLs)大肠埃希菌和肺炎克雷伯菌的检出率逐年增高,2003年广东地区产ESBL 大肠埃希菌和肺炎克雷伯菌的检出率分别为29.6％和30.1％,辽宁地区的检出率分别为18．6％和26．6％。广东和辽宁地区的大肠埃希菌和肺炎克雷伯菌临床分离株头孢噻肟耐药、头孢他啶敏感率明显高于头孢噻肟敏感、头孢他啶耐药率。结论通过不同地区间临床分离株细菌耐药性的比较,了解耐药率间的差别,对于临床合理使用抗菌药物、有效控制耐药菌株的传播具有重要意义。     

Acquired sulphonamide resistance genes in faecal Escherichia coli from healthy children in Bolivia and Peru

Antimicrobial resistance and sulphonamide resistance determinants were studied in 20 co-trimoxazole resistant Escherichia coli in faecal samples from healthy children in Bolivia and Peru. Methods used were disc diffusion susceptibility tests, PCR, sequence analysis and plasmid conjugation assays. All isolates but one were resistant to at least two different classes of antimicrobials; 19 isolates also carried at least one sul-gene. The most frequent gene was sul2 followed by sul1 and sul3, which was detected in one isolate. This is the first observation of sul3 on the American continent. In conclusion, the high prevalence of sul-genes in this material of faecal commensal E. coli isolates points to a potential role of the faecal flora in the emergence and spread of antimicrobial resistance.     

Complete nucleotide sequence of the gyrA gene of Helicobacter pullorum and identification of a point mutation leading to ciprofloxacin resistance in poultry isolates

To assess the molecular basis of nalidixic acid and ciprofloxacin resistance in Helicobacter pullorum, the gyrA gene of H. pullorum CIP 104787T was sequenced. In addition, 9 isolates (2 susceptible to ciprofloxacin and resistant to nalidixic acid, 3 susceptible and 4 resistant to both antibiotics) were selected from 44 poultry isolates and the nucleotide sequences of their quinolone resistance-determining regions (QRDRs) were compared. The 2490 bp gyrA gene showed an open reading frame encoding a polypeptide of 829 amino acids. The deduced amino acid sequence of gyrA showed>or=72% identity to Helicobacter hepaticus, Helicobacter pylori and Wolinella succinogenes. Moreover, >or=98% amino acid sequence identity was found comparing the QRDR of the H. pullorum type strain with the QRDRs of the aforementioned bacterial species. All ciprofloxacin-resistant poultry isolates showed an ACA-->ATA (Thr-->Ile) substitution at codon 84 of gyrA, corresponding to codons 86, 87 and 83 of Campylobacter jejuni, H. pylori and Escherichia coli gyrA genes, respectively. This substitution was functionally confirmed to be associated with the ciprofloxacin-resistant phenotype of poultry isolates. This is the first report describing the complete 2490 bp nucleotide sequence of H. pullorum gyrA and confirming the involvement of the Thr84Ile substitution of GyrA in ciprofloxacin resistance of H. pullorum.     

Efflux pump genes and antimicrobial resistance of Pseudomonas aeruginosa strains isolated from lower respiratory tract infections acquired in an intensive care unit

The aim of this study was to determine the antimicrobial resistance rates and the resistance genes associated with efflux pumps of Pseudomonas aeruginosa strains isolated from the patients who acquired lower respiratory tract infection (LRTI) in intensive care unit (ICU). Fifty P. aeruginosa strains isolated from the lower respiratory tract specimens of the patients who acquired LRTIs in ICU were included in this study. P. aeruginosa strains were isolated from tracheal aspirate (27), bronchoalveolar lavage (14) and sputum (9). The susceptibilities of the isolates were investigated by the disk diffusion method. Multiplex PCR assay was carried out for the detection of 13 antibiotic-resistance genes. Antimicrobial resistance rates of the isolates were found high and the highest resistance rate of the isolates studied was determined against to mezlocillin (50%) followed by norfloxacin (48%), ciprofloxacin (46%), meropenem (40%). Fourty-three isolates (86%) were determined to carry one and more resistance genes. NfxB gene was most often determined in the genes that were investigated. The significant relation between the resistance to cefepime, piperacilline/tazobactam and the mexC gene, that between the resistance to mezlocillin, piperacilline/tazobactam, ceftazidime, cefepime and ampC genes, and that between the resistance to ciprofloxacin, norfloxacin and oprJ, oprN and nfxB genes was identified. Resistance caused by genes for carbapenemases, aminoglycoside-modifying enzymes and other mechanisms were not identified in this study. Understanding the prevalence and mechanism of antimicrobial resistance in P. aeruginosa may help to select empirical therapy for nosocomial LRTIs due to P. aeruginosa in our ICU.     

High levels of multidrug resistance in clinical isolates of Gram-negative pathogens from Nigeria

In Nigeria, quinolones and β-lactam antibiotics are widely used to treat bacterial infections. This study aimed to identify the prevalence of resistance to these drugs and to determine the mechanisms of resistance to these agents. In total, 134 non-duplicate, Gram-negative enteric isolates of 13 species from different hospitals were investigated for susceptibility to a panel of antibiotics, carriage of plasmid-mediated quinolone and β-lactam resistance genes, production of extended-spectrum β-lactamases (ESBLs), and mutations within topoisomerase genes. The level of resistance to all antibiotics tested was extremely high, with minimum inhibitory concentrations for 90% of the organisms (MIC(90) values) of ≥ 256 μg/mL for all drugs. Of the 134 isolates, 92 had mutations within the quinolone resistance-determining region (QRDR) of gyrA or within gyrA and parC. In addition, the plasmid-mediated quinolone resistance genes qnrA, qnrB, aac(6')-Ib-cr and qepA were identified. The qnrD allele, which has previously only been found in Salmonella isolates from China, was identified in two Proteus isolates and one Pseudomonas isolate. Of the 134 isolates, 23 (17.2%) carried aac(6')-Ib-cr, 11 (8.2%) carried a qnr variant and 5 (3.7%) were positive for qepA. Twenty-eight isolates (20.9%) produced ESBL variants, with a CTX-M variant being carried by 25 isolates (18.7%). In addition, six isolates (4.5%) carried ampC variants [ACT-1 (1 isolate), DHA-1 (4 isolates) and CMY-2 (1 isolate)]. This study demonstrates a very high level of multidrug resistance amongst Gram-negative enteric bacilli isolated from different sites from patients in Nigerian hospitals as well as the presence of a variety of plasmid-associated resistance genes, including some identified from Africa for the first time.     

Recognition of mechanisms involved in bile resistance important to halting antimicrobial resistance in nontyphoidal Salmonella

Increasing antimicrobial resistance in nontyphoidal Salmonella (NTS) is a global public health problem that complicates antimicrobial therapy. As an enteric pathogen, Salmonella must endure the presence of bile in the intestinal tract during the course of infection. In this study, we sought to identify Salmonella genes necessary for bile resistance and to investigate their association with antimicrobial resistance. Four genes related to bile resistance were identified, namely rfaP, rfbK, dam and tolC. The first three genes are involved in lipopolysaccharide synthesis, and tolC is associated with an efflux pump. Antimicrobial susceptibility testing showed increased susceptibility to polymyxin B and ciprofloxacin in rfaP and tolC mutants of Salmonella, respectively. Genetic analysis of 45 clinical isolates of NTS revealed that all isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration ≥0.125 mg/L) were associated with point mutations in the quinolone resistance-determining regions of the gyrA and parC genes. The efflux pump also played a role, as evidenced by the reduction in fluoroquinolone resistance when the TolC efflux pump was inhibited by Phe-Arg-β-naphthylamide, a competitive efflux pump inhibitor. Based on these results, we conclude that an intact membrane structure and the efflux pump system provide mechanisms enabling NTS to resist bile. Caution should be taken when using ciprofloxacin and polymyxin B to treat Salmonella enteric infection, as resistance to these agents involves the same mechanisms. Addition of an efflux pump inhibitor to fluoroquinolones may be an effective strategy to deal with the increasing resistance in NTS.