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首页> 外文学位 >The regulation of expression of the Stx2d toxins in shiga toxin-producing Escherichia coli O91:H21 strain B2F1.
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The regulation of expression of the Stx2d toxins in shiga toxin-producing Escherichia coli O91:H21 strain B2F1.

机译：产志贺毒素的大肠杆菌O91：H21菌株B2F1中Stx2d毒素表达的调节。

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摘要

Shiga toxin (Stx) types 1 and 2 are encoded within intact or defective temperate bacteriophages in Stx-producing Escherichia coli (STEC), and expression of these toxins is linked to bacteriophage induction. Among Stx2 variants, only stx2e from one human STEC isolate has been reported to be encoded within a toxin-converting phage. In this study, I examined O91:H21 STEC isolate B2F1 that carries two functional alleles (stx2d1 and stx 2d2) for the potent activatable Stx2 variant toxin, Stx2d, for the presence of Stx2d-converting bacteriophages and other potential regulators of toxin expression. Mutants of B2F1 that produced one or the other Stx2d toxin were made. The Stx2d1-producing mutant (stx2d2:: cat) was less cytotoxic for Vero cells than the Stx2d2-producing mutant (stx2d1::cat). Consistent with those results, the Stx2d1-producing mutant was attenuated in a streptomycin-treated mouse model of STEC infection, while the Stx2d2-producing mutant was nearly as virulent as wild-type B2F1. When the mutants were treated with mitomycin C to promote bacteriophage induction, Vero cell cytotoxicity was elevated only in extracts of the Stx2d1-producing mutant. Additionally, when mice were treated with ciprofloxacin, an antibiotic that induces the O157:H7 Stx2-converting phage, the animals were more susceptible to the Stx2d1-producing mutant. An stx2d1-containing lysogen was isolated from plaques on strain DH5alpha that had been exposed to lysates of the mutant that produced Stx2d1 only. However, that RecA- lysogen could not be induced for phage nor were culture lysates from it cytotoxic for Vero cells. By contrast, when the lysogen was transformed with a plasmid encoding RecA and induced with mitomycin C, culture extracts were cytotoxic for Vero cells. Furthermore, electron microscopic examination of extracts from the &phis;B2F1-lysogen showed hexagonal particles that resembled the prototypic Stx2-converting phage 933W. These observations provide strong evidence that expression of Stx2d1 is bacteriophage-associated.;The finding that synthesis of Stx2d1 but not Stx2d2 was associated with phage induction led me to investigate regulation of Stx2d2 production. Transposon mutagenesis of DH5alpha revealed genes associated with reduced expression of an stx2d2 promoter::lacZ fusion in a reporter plasmid, observations that suggested the inactivation of potential activators of transcription of stx2d2. (Abstract shortened by UMI.)
机译：1型和2型志贺毒素（Stx）在产Stx的大肠杆菌（STEC）的完整或有缺陷的温带噬菌体中编码，这些毒素的表达与噬菌体诱导有关。在Stx2变体中，据报道只有一种人STEC分离株的stx2e被编码在毒素转化噬菌体中。在这项研究中，我检查了O91：H21 STEC分离株B2F1，该分离株携带两个有效等位基因（stx2d1和stx 2d2）的有效可激活Stx2变体毒素Stx2d，其中存在Stx2d转化噬菌体和其他可能的毒素表达调节剂。产生了产生一种或另一种Stx2d毒素的B2F1突变体。产生Stx2d1的突变体（stx2d2 :: cat）对Vero细胞的细胞毒性比产生Stx2d2的突变体（stx2d1 :: cat）低。与这些结果一致，在链霉素处理的STEC感染小鼠模型中，产生Stx2d1的突变体减毒，而产生Stx2d2的突变体的毒性几乎与野生型B2F1相同。当用丝裂霉素C处理突变体以促进噬菌体诱导时，仅在产生Stx2d1的突变体的提取物中提高了Vero细胞的细胞毒性。此外，当用环丙沙星（一种诱导O157：H7 Stx2转化噬菌体的抗生素）对小鼠进行治疗时，动物对产生Stx2d1的突变体更敏感。从已暴露于仅产生Stx2d1的突变体的裂解物中的菌株DH5alpha的噬菌斑中分离出含stx2d1的溶原原。但是，RecAlysogen不能被噬菌体诱导，培养的裂解液也不能对Vero细胞产生细胞毒性。相反，当溶菌原用编码RecA的质粒转化并用丝裂霉素C诱导时，培养物提取物对Vero细胞具有细胞毒性。此外，对来自B 2 F 1-溶原原的提取物的电子显微镜检查显示出类似于原型Stx 2转化噬菌体933W的六角形颗粒。这些观察结果提供了有力的证据，表明Stx2d1的表达与噬菌体有关。Stx2d1的合成而不是Stx2d2的合成与噬菌体诱导有关的发现使我研究了Stx2d2产生的调控。 DH5α的转座子诱变揭示了与报道质粒中stx2d2启动子:: lacZ融合蛋白表达降低相关的基因，这些发现提示stx2d2转录的潜在激活因子失活。 （摘要由UMI缩短。）

著录项

  • 作者

    Teel, Louise Davis.;

  • 作者单位

    Uniformed Services University of the Health Sciences.;

  • 授予单位 Uniformed Services University of the Health Sciences.;
  • 学科 Biology Microbiology.;Health Sciences Immunology.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 151 p.
  • 总页数 151
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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