Molecular epidemiology of cytolethal distending toxin-producing Escherichia coli

我们已经证明cdtB基因在肠致病性大肠杆菌（EPEC）中被特异性鉴定。一些菌株与引起儿童出血性腹泻有关，并表现出更高的CDT产量。cdtB阳性菌株主要属于O86a和O127a血清群。脉冲场凝胶电泳图谱显示，携带ctdB的EPEC菌株具有遗传多样性。本研究对1607份粪便标本进行了肠道病原体cdtB筛查。探针杂交检测6份（0.4%）阳性，PCR检测5株。从cdtB探针或PCR阳性样品中仅分离出大肠杆菌，并经血清学证实。6株中4株鉴定为O142血清群。对这些菌株进行不同致泻性大肠杆菌毒力基因的鉴定表明，6株菌株是肠致病性大肠杆菌（EPEC），它们携带eae和bfp基因。我们在早期的报告中也报告了同样的趋势。除了两个，所有的菌株都含有cdtA和cdtC基因。这两株菌株经PCR检测均为cdtB阴性，在组织培养试验中均不表达CDT。根据氨基酸序列的变化，Cdt可分为CdtI、CdtII和CdtIII。目前，我们正在分析所有菌株以检测Cdt等位基因。临床和细菌学研究表明，部分肠道微生物坏死的大肠杆菌产生粘菌素与胃肠道炎症性疾病的临床表现有关。大肠杆菌素在许多肠道病原菌中表达，特别是在肠致病性大肠杆菌（EPEC）和肠出血性大肠杆菌（EHEC）中。18株中有3株（16.7%）表达Colicin。血清组与大肠杆菌素表达无相关性。

We have shown that cdtB gene was specifically identified among enteropathogenic E.coli(EPEC). Some of the strains are associated in causing bloody diarrhea among children and exhibited higher production of CDT. The cdtB positive strain mostly belongs to O86a and O127a serogroups. Pulsed-field gel electrophoresis profiles showed that the EPEC strains harboring ctdB were genetically diverse.In this study, 1607 stool specimens were screened for the cdtB harboring enteric pathogens. In the probe hybridization assay, 6 samples (0.4%) were positive and the PCR assay confirmed 5 strains. Form the cdtB probe or PCR positive samples only E.coli strains were isolated and confirmed by serology. Four out of six strains were identified as serogroup O142. Characterization of these strains for different virulence genes specific for diarrheagenic E.coli showed that six strains were enteropathogenic E.coli(EPEC), as they harbored eae as well as bfp genes. We have reported the same trend in our early reports.Expect for two, all the strains harbored cdtA and cdtC genes. These two strains were negative for cdtB by PCR and did not express the CDT in the tissue culture assay. Based on the variation in the sequence of amino acids, the Cdt is classified into CdtI, CdtII and CdtIII. Currently, we are analyzing all our strains to detect the Cdt alleles.Clinical and bacteriological studies have revealed that production of colicin by E.coli having a part of intestinal microbiocenasis is related to the clinical manifestation of inflammatory disease of the gastrointestinal tract. Colicin expression was determined in many enteric pathogens especially among enteropathogenic E.coli(EPEC) and enterohemorrhagic E.coli(EHEC). Colicin expression was confirmed with 3 out of 18 strains (16.7%). There is no correlation between serogroups and colicin expression.