多重PCR-DHPLC技术检测肠出血性大肠杆菌O157:H7基因型的方法学研究

目的 开发肠出血性大肠杆菌O157:H7的多重PCR-变性高效液相色谱(DHPLC)检测方法 .方法 以编码大肠杆菌0157抗原的rfbE 基因、编码毒力因子的类志贺毒素(SLT)基因为目的 基因,选择2对引物,建立并优化了大肠杆菌O157:H7的多重PCR-DHPLC检测体系.扩增产物分别为224 bp和499 bp.结果 采用37株细菌验汪了该多重PCR具有良好的特异件.PCR榆测的灵敏度可达到4 CFU/ml.结论 实验证明,研究建立的多重PCR-DHPLC方法 可特异、灵敏地实现对大肠杆菌O157:H7的检测.     

肠出血性大肠杆菌O157:H7溶血素保护性片段(HlyAN436)克隆、表达、初步纯化与生物学活性研究

目的获取重组表达肠出血性大肠杆菌O157的溶血素（Ehx）保护性片段，并研究其基本的生物学及免疫学特性。方法PCR法从EHECO157-SMR2菌株克隆O157：H7的HlyA亚单位的N端片段（436个氨基酸），T-A克隆后构建表达载体pET-28a（＋）-HlyAN436，测序鉴定后转化到E.coliBL21（DE3），IPTG诱导表达，初步纯化后免疫动物。结果Hly-AN436成功地在大肠杆菌表达系统表达，动物实验证实其具有良好的免疫原性和反应性以及一定的免疫保护性。结论Hly-AN436蛋白有可能用于肠出血性大肠杆菌O157基因工程疫苗的研究。     

肠出血性大肠杆菌O157:H7外膜蛋白A敲除菌株的构建及其黏附作用研究

目的利用Red同源重组技术构建肠出血性大肠杆菌(EHEC)O157∶H7外膜蛋白A(ompA)基因敲除菌株,研究敲除菌株的黏附能力变化,阐明OmpA在细菌黏附以及致病中的作用。方法利用Red同源重组技术对EHEC O157∶H7 ompA基因进行敲除,同时构建EHEC O157:H7 ompA回复突变菌株,最后通过细胞试验对EHEC O157∶H7野生型菌株、敲除菌株及回复突变菌株的黏附能力进行比较。结果成功构建了EHEC O157:H7 ompA基因敲除菌株及其回复突变菌株。细胞试验结果表明,与野生型菌株相比,敲除菌株的黏附能力明显下降,而将ompA基因进行回复突变后其黏附能力又得到回复。结论 OmpA在EHEC O157∶H7黏附HeLa细胞过程中发挥重要作用,ompA基因敲除菌株的获得为进一步研究其功能提供了帮助。     

抗肠出血性大肠杆菌O157:H7 EspA单克隆抗体的制备及其特性鉴定

目的:制备抗肠出血性大肠杆菌O157:H7EspA单克隆抗体(mAb)。方法:以重组EspA蛋白为免疫原免疫BALB/c小鼠,运用杂交瘤技术并且联合间接ELISA筛选只针对EspA的杂交瘤细胞株。以Ig类与亚类鉴定试剂盒鉴定mAb的Ig亚类,ELISA、Western blot及免疫荧光技术鉴定抗体的免疫学特性。结果:获得3株稳定分泌抗EspA杂交瘤细胞的mAb,Ig亚型分别为IgG1κ型、IgG2aκ型、IgG2bκ型。Western blot和免疫荧光分析表明,3株杂交瘤细胞制备的mAb腹水都能特异地结合重组EspA蛋白和识别O157:H7的EspA成分。结论:成功地制备了抗肠出血性大肠杆菌O157:H7EspA的mAb,并证明了该mAb的生物学活性,为深入研究肠出血性大肠杆菌O157:H7的致病机制提供新的手段。     

产志贺毒素大肠杆菌O157∶H7的亚碲酸钾抗性基因簇分布和抗性水平

目的 了解产志贺毒素大肠杆菌O157：H7的亚碲酸盐抗性基因簇的分布和抗性水平的关系。方法运用PCR和核酸杂交方法进行基因检测，使用平皿法检测亚碲酸钾抗性水平。结果在所检测的志贺菌、沙门菌、霍乱弧菌、耶尔森菌、泌尿道致病性大肠杆菌、肠产毒性大肠杆菌、肠致病性大肠杆菌、肠侵袭性大肠杆菌、肠黏附性大肠杆菌、肠出血性大肠杆菌中，只有大肠杆菌O157：H7具有ter(tellurite resistance，ter)基因簇。所检测的34株产志贺毒素的大肠杆菌O157：H7有33株具有ter基因簇，所检测的18株不产生志贺毒素的大肠杆菌O157，4株具有ter基因簇，但是没有该毒力岛的其它基因。ter基因阳性的33株菌中，亚碲酸钾的抗性水平一般较高，4株在750μg/ml以上，19株为500～750μg/ml，10株为250～500μg/ml；而4株ter基因簇阴性的菌株，也表现了高水平的耐药性，其抗性水平均为500～750μg/ml。其它ter基因簇阴性的菌株，20株耐药性为5～10μg/ml，1株10～20μg/ml，6株20～50μg/ml，2株50～100μg/ml，1株100～250μg/ml。结论ter基因簇在产志贺毒素的大肠杆菌O157：H7中高频率存在，而在其它病原菌中没有检测到。高水平的亚碲酸钾抗性可以作为选择性分离产志贺毒素大肠杆菌O157：H7的指标之一。     

抗出血性大肠杆菌O157:H7单克隆抗体的制备及初步应用

1983年美国Riley等~([1])首次报道肠出血性大肠杆菌O157:H7,我国于1987年首次在出血性肠炎患者体内分离到大肠杆菌O157:H7.     

单核细胞增生李斯特菌与志贺菌双重实时PCR检测技术的建立

目的 建立一种快速、特异、灵敏、准确定量的单核细胞增生(单增)李斯特菌(Listeriamonocytogenes)与志贺菌(Shigella)同步检测方法.方法 分别根据单增李斯特菌溶血素O基因hly与志贺菌侵袭性质粒抗原H基因ipaH设计合成引物和探针.构建重组质粒pGEM-T-hly与pGEM-T-ipaH,并以EcoR I单酶切使环状重组质粒线性化作为标准品.优化反应体系,分析特异性.双重荧光定量PCR对人工污染的脱脂灭菌乳进行检测.结果 成功构建了重组质粒标准品,并运用5'、3'端分别标记FAM、TAMRA的hly基因探针和5'、3'端分别标记HEX、TAMRA的ipaH基因探针成功建立了单增李斯特菌与志贺菌同步荧光定量PCR检测方法.结论 建立的方法有较强的特异性,线性范围好(105～101copies/μl,R2≥0.998),灵敏度为10 copies/PCR,同步检测人工污染脱脂灭菌乳的灵敏度为102CFU/ml.     

应用酶联免疫吸附试验检测肠出血性大肠杆菌O157:H7

目的制备和纯化O157：H7抗原，免疫家兔和豚鼠，获得高效价的抗O157：H7免疫血清并进行纯化及酶标记。建立对O157：H7感染患者快速诊断方法，做到早期发现及时治疗，有效控制疫情的蔓延。方法ELISA双抗体夹心法检测O157：H7抗原。步骤：包被特异性抗体，加处理后的粪便等标本，然后加入抗O157：H7酶结合物，最后加入底物显色。结果本课题所研制的抗O157：H7酶结合物只对O157：H7呈阳性反应，而与其他相关细菌无交叉反应。结论应用酶联免疫吸附试验(即双抗体夹心法)对肠出血性大肠杆菌O157：H7抗原的检测较常规法实验程序简捷、快速、敏感。临床和现场验证结果表明，其方法具有灵敏度高，特异性强操作简单等特点，为肠出血性大肠杆菌O157：H7的鉴定及快速诊断提供了一种新的检测手段。     

肝螺杆菌TaqMan MGB探针实时荧光定量PCR快速检测方法的建立及应用研究

目的 建立特异、敏感、快速检测肝螺杆菌的TaqMan MGB探针实时荧光定量PCR方法.方法 针对肝螺杆菌flaB 基因的保守区设计特异性引物和探针,建立肝螺杆菌TaqMan MGB探针实时荧光定最PCR方检测方法,验证方法的特异性、敏感性和稳定性.对2008-2011年期间采集的1081份临床样本中的肝螺杆菌进行检测,同时进行分离培养和常规PCR检测.结果 建立的TaqMan MGB探针实时荧光定量PCR方法对肝螺杆菌的检测具有高度的特异性,对幽门螺杆菌、空肠弯曲菌、泰泽氏菌、侵肺巴斯德氏菌、大肠埃希菌、铜绿假单胞菌均无交叉反应,检测的灵敏度达8.3拷贝.标准曲线显示各浓度范围内具有良好的线性关系,相关系数为0.999,斜率为-3.227,TaqManMGB探针实时荧光定量PCR效率为100％.对1081份临床样本进行检测,TaqMan MGB探针实时荧光定量PCR和常规PCR均能检出86份肝螺杆菌阳性样本,而细菌分离培养则仅检出4份阳性.结果显示,建立的TaqMan MGB探针实时荧光定量PCR方法比细菌分离培养方法更敏感,能够直接从临床样本中检出肝螺杆菌DNA,检测时间仅为2h.结论 研究建立的TaqMan MGB探针实时荧光定量PCR方法具有可靠、特异、敏感的特点,适用于肝螺杆菌的快速检测.     

实时荧光RT-PCR检测活性单核细胞增生李斯特菌方法的建立

目的 采用逆转录结合实时荧光定量PCR技术,建立一种快速、准确、特异甄别单核细胞增生李斯特菌(Listeria monocytogenes,简称单增李氏菌)死活状态的定量方法.方法 根据单增李氏菌hlyA基因序列设计引物和探针;对实时荧光PCR反应体系进行优化后,提取菌体mRNA,通过随机引物进行逆转录反应;产生的cDNA通过实时荧光定量PCR进行鉴定.进一步评价逆转录结合实时荧光定量PCR方法的特异性、灵敏度、重复性后,对20份模拟双盲样本进行检测.结果 本实验所建立的逆转录结合实时荧光定量PCR方法可准确、特异地检测单增李氏菌,其他菌株和失活的单增李氏菌均无阳性结果出现;该方法检测纯菌和模拟样本的灵敏度分别可达到10 CFU/ml和1000CFU/ml;定量检测的批间和批内的变异系数均小于5%;对20份模拟样本进行检测,其中10份含有活性单增李氏菌样本的检测结果均为阳性,其他含有失活单增李氏菌的5份样本和其他致病菌的5份样本检测结果为阴性.结论 本文建立的检测活性单增李氏菌实时荧光定量PCR方法快速、准确,结果可靠,实用性强,可进行定量分析,为食品安全监测和现场流行病学调查提供较好的分析手段和完整的数据.     

Simultaneous identification of strains of Escherichia coli serotype O157:H7 and their Shiga-like toxin type by mismatch amplification mutation assay-multiplex PCR.

Mismatch amplification mutation assay primers, specific for a unique base substitution in uidA of Escherichia coli O157:H7, was coupled with primers for the Shiga-like toxin I (SLT-I) and SLT-II genes in a multiplex PCR assay. Analysis of 108 bacteria showed that all Escherichia coli serotype O157:H7 strains were identified simultaneously with the SLT types encoded by these strains.     

Use of the duplex TaqMan PCR system for detection of Shiga-like toxin-producing Escherichia coli O157

Real-time PCR assays have been applied for the detection and quantification of pathogens in recent years. In this study two combinations of primers and fluorescent probes were designed according to the sequences of the rfb(Escherichia coli O157) and stx2 genes. Analysis of 217 bacterial strains demonstrated that the duplex real-time PCR assay successfully distinguished the Escherichia coli O157 serotype from non-E. coli O157 serotypes and that it provided an accurate means of profiling the genes encoding O antigen and Shiga-like toxin 2. On the other hand, bacterial strains that lacked these genes were not detected by this assay. The quantitative ranges of the real-time PCR assay for these two genes were linear for DNA concentrations ranging from 10(3) to 10(9) CFU/ml of E. coli O157:H7 in pure culture and milk samples. The real-time PCR allowed the construction of standard curves that facilitated the quantification of E. coli O157:H7 in feces and apple juice samples. The detection sensitivity of the real-time PCR assay ranged from 10(4) to 10(9) CFU/g (or 10(4) to 10(9) CFU/ml) for feces and apple juice and 10(5) to 10(9) CFU/g for the beef sample without enrichment. After enrichment of the food samples in a modified tryptic soy broth, the detection range was from 10(0) to 10(3) CFU/ml. The real-time PCR assays for rfb(E. coli) (O157) and stx2 proved to be rapid tests for the detection of E. coli O157 in food matrices and could also be used for the quantification of E. coli O157 in foods or fecal samples.     

Genetic analysis for virulence factors in Escherichia coli O104:H21 that was implicated in an outbreak of hemorrhagic colitis

Isolates of enterohemorrhagic Escherichia coli (EHEC) of serotype O104:H21 implicated in a 1994 outbreak of hemorrhagic colitis in Montana were analyzed for the presence of trait EHEC virulence markers. By using a multiplex PCR that specifically amplifies several genes, the O104:H21 strains were found to carry only the Shiga toxin 2 gene (stx2) and to express Stx2. They did not have the eaeA gene for gamma-intimin, which is typically found in O157:H7, or the alpha- or beta-intimin derivatives, which are common in other EHEC and enteropathogenic E. coli serotypes. Results of the multiplex PCR also indicated that the ehxA gene for enterohemolysin was absent from O104:H21. This, however, was not consistent with the results of a phenotypic assay that showed them to be hemolytic or a PCR analysis with another set of ehxA-specific primers, which indicated the presence of ehxA. To resolve this discrepancy, the ehxA region in O104:H21 and O157:H7 strains, to which the multiplex PCR primers anneal, was cloned and sequenced. Comparison of the sequences showed that the upstream primer binding site in the ehxA gene of O104:H21 was not identical to that of O157:H7. Specifically, there were several base mutations, including an A-to-G substitution at the 3' end of the primer binding site. These base mutations are presumably not unique to O104:H21, since other enterohemolytic serotypes were also not detected with the ehxA primers used in the multiplex PCR. Comparison of the ehxA sequences of O104:H21 strains with those of other Stx-producing E. coli strains showed that they more closely resembled those of O8:H19 strains, which have cluster II ehxA genes, than those of O157:H7 strains, which have cluster I ehxA sequences. By modifying the upstream ehxA primer, the multiplex PCR was able to detect ehxA genes in both O157:H7 and O104:H21 strains.     

Detection of Escherichia coli O157:H7 by multiplex PCR.

In order to develop a PCR assay for Escherichia coli O157:H7, a portion of the 60-MDa plasmid harbored by enterohemorrhagic E. coli (EHEC) was sequenced and PCR primers were designed. A multiplex PCR method was then designed by employing primers specific for the EHEC eaeA gene, conserved sequences of Shiga-like toxins I (SLT-I) and II (SLT-II), and the 60-MDa plasmid. PCR products of 1,087 bp (eaeA), 227 and/or 224 bp (SLT-I and/or SLT-II), and 166 bp (plasmid) were successfully amplified simultaneously in a single reaction. The multiplex PCR method can be used to specifically identify EHEC of serogroup O157.     

PCR for specific detection of H7 flagellar variant of fliC among extraintestinal pathogenic Escherichia coli

A newly developed PCR-based assay for the H7 variant of the Escherichia coli flagellin gene, fliC, was 100% sensitive and specific in comparison with serology and probe hybridization. It revealed broad conservation of the H7 fliC variant among phylogenetically diverse lineages of extraintestinal pathogenic E. coli (ExPEC) and superseded serotyping for certain isolates with ambiguous or non-H7 serotyping results. The H7 primers functioned well when incorporated into a multiplex PCR assay for diverse virulence-associated genes of ExPEC.     

Antibodies to Escherichia coli O157 in patients with haemorrhagic colitis and haemolytic uraemic syndrome.

Twenty four sera from patients with haemolytic uraemic syndrome or haemorrhagic colitis and healthy controls were examined for antibodies to the lipopolysaccharide (LPS) of Escherichia coli O157. Faecal specimens from these patients were also examined for Vero cytotoxin producing E coli (VTEC) by DNA probes, and for faecal Vero cytotoxin. Eight patients with faecal E coli O157:H7 gave a strong antibody response to O157 LPS, shown by immunoblotting and an enzyme linked immunosorbent assay. Six symptomatic patients without evidence of faecal VTEC also gave a strong antibody response to O157 LPS. Sera from the remaining five patients and five healthy controls did not contain antibodies to E coli O157. The results suggest that the testing of sera from patients with haemorrhagic colitis or haemolytic uraemic syndrome by ELISA or immunoblot would prove valuable in addition to the established procedures for detecting VTEC, using DNA probes and testing for faecal Vero cytotoxin.     

化学发光磁酶免疫法检测O157:H7大肠埃希菌

目的：建立灵敏稳定检测O157：H7大肠埃希菌的化学发光磁酶免疫法.方法：利用AMPPD-ALP化学发光体系,通过磁珠酶联免疫法对O157：H7大肠埃希菌进行检测.结果：其检测灵敏度达到850个,线性范围为1 000～50 000个,批间变异小于15%,批内变异小于20%,与人工计数培养检测相比相关系数达0.9807.结论：化学发光磁酶免疫分析法操作简便,检测精密度和灵敏度高,是一种很有发展前景的可靠方法.     

Determination of verocytotoxin and eae gene loci by multiplex PCR in Escherichia coli O157:H7 isolated from human faeces in Northern Ireland: a four-year study of trends, 1997-2000

This study aims to determine the distribution and frequency of verocytotoxin genes in human faecal clinical isolates of Escherichia coli O157 in Northern Ireland during the period 1997-2000, using a special four-target multiplex polymerase chain reaction (PCR) assay. One hundred and thirty two isolates of E. coli O157:H7 cultured during the four-year period (1997 [n=28]; 1998 [n=25]); 1999 (n=43); 2000 [n=36]), representing approximately 79% of total E. coli O157 laboratory isolations throughout N. Ireland, are examined for the presence of verocytotoxin gene loci (VT1, VT2 and eae) using a multiplex PCR assay. These isolates originate from the four Regional Area Health Boards that constitute the healthcare system in N. Ireland as follows: Eastern (53.8%; n=71), Northern (34.1%; n=45), Western (6.8%; n=9) and Southern (5.3%; n=7). Results showed that over 80% of these isolates possessed the VT2 and eae gene loci, with the remainder being predominantly VT1-, VT2- and eae-positive. None possessed the VT1 gene locus alone. Development and adoption of this simple four-target (three virulence and one control gene loci) multiplex PCR assay and subsequent recording of resulting verocytotoxin-typing data in a database, permitted local, rapid determination of carriage of known molecular virulence determinants of E. coli O157 isolates, which may aid in outbreak-related epidemiological investigations or other longitudinal studies.     

Comparison between O serotyping method and multiplex real-time PCR to identify diarrheagenic Escherichia coli in Taiwan

To compare the diarrheagenic Escherichia coli (DEC) identifications obtained between traditional O serotyping and modern virulence gene detection assays, we developed a multiplex real-time PCR assay by detecting six specific virulence genes for enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enterotoxigenic E. coli (ETEC), and enteroinvasive E. coli (EIEC). Among 261 clinical diarrheal stool samples, a total of 137 suspected DEC (sDEC) isolates were identified by the use of commercially available antisera. The most prevalent serogroups were O1 (12/137; 8.7%), O25 (9/137; 6.5%), and O44 (9/137; 6.5%). The specific virulence genes for the 137 sDEC isolates were analyzed by the multiplex real-time PCR assay. Fifteen (10.9%) of 137 isolates were confirmed to be true DEC strains, indicating that the serotypic markers did not correlate with the specific virulence genes. ETEC (66.7%) was the most prevalent, followed by EIEC (20%) and EPEC (13.3%). No EHEC strains were identified in the specimens. Four novel serotypes were found in the study: two in EPEC strains (O111:H9 and O63:H6) and two in EIEC strains (O63:H9 and O169:H9). In conclusion, the real-time PCR assay considerably reduces the high false-positive rate from the use of serotyping alone, and thus, it is suggested that serogrouping-based methods are inadequate for the identification of DEC isolates, although they are useful for the identification of a limited number of serogroups. In addition, ETEC, EPEC, and EIEC strains were present in 5.7% (15/261) of the diarrheal patients in northern Taiwan in 2006.     

Detection of Eschericia coli O157:H7 by fluorescence polarization assay and polymerase chain reaction

It is recognized that cattle and other domestic animals can be a reservoir of pathogenic Escherichia coli, including serotype O157:H7. To contain this potential health hazard, the first step is the identification of the carrier animals. For these purposes, a rapid serological screening test, a fluorescence polarization assay (FPA) was developed and results obtained from a randomly selected cattle population as well as cattle immunized with E. coli O157:H7 were compared to those obtained with an indirect enzyme immunoassay (IELISA). To identify pathogenic strains in carrier animals, polymerase chain reactions (PCR) for Shiga-like toxins I and II were implemented using agarose electrophoresis. The sensitivity of the fecal extracted E. coli for Shiga-like toxin I and II was approximately 200 CFU per reaction using multiplex hot-start nested PCR. The sensitivity of the fecal extracted E. coli varied from approximately 5x10(2) to 2.5x10(3) CFU per reaction depending on the commercial kits used. The combination of the serological screening FPA and hot-start nested PCR confirmatory assays provided rapid identification of the pathogen.