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首页> 外文期刊>Infection and immunity >One of Two Copies of the Gene for the Activatable Shiga Toxin Type 2d in Escherichia coli O91:H21 Strain B2F1 Is Associated with an Inducible Bacteriophage
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One of Two Copies of the Gene for the Activatable Shiga Toxin Type 2d in Escherichia coli O91:H21 Strain B2F1 Is Associated with an Inducible Bacteriophage

机译：大肠杆菌O91：H21菌株B2F1中2d型可活化志贺毒素基因的两个副本之一与可诱导噬菌体相关

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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 carried within a toxin-converting phage. In this study, we examined the O91:H21 STEC isolate B2F1, which carries two functional alleles for the potent activatable Stx2 variant toxin, Stx2d, for the presence of Stx2d-converting bacteriophages. We first constructed mutants of B2F1 that produced one or the other Stx2d toxin and found that the mutant that produced only Stx2d1 made less toxin than the Stx2d2-producing mutant. Consistent with that result, the Stx2d1-producing mutant was attenuated in a streptomycin-treated mouse model of STEC infection. 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. Moreover, an stx2d1-containing lysogen was isolated from plaques on strain DH5α that had been exposed to lysates of the mutant that produced Stx2d1 only, and supernatants from that lysogen transformed with a plasmid encoding RecA were cytotoxic when the lysogen was induced with mitomycin C. Finally, electron-microscopic examination of extracts from the Stx2d1-producing mutant showed hexagonal particles that resemble the prototypic Stx2-converting phage 933W. Together these observations provide strong evidence that expression of Stx2d1 is bacteriophage associated. We conclude that despite the sequence similarity of the stx2d1- and stx2d2-flanking regions in B2F1, Stx2d1 expression is repressed within the context of its toxin-converting phage while Stx2d2 expression is independent of phage induction.
机译：1型和2型志贺毒素（Stx）分别在产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 stx 2e 携带在毒素转化噬菌体中。在这项研究中，我们检查了O91：H21 STEC分离株B2F1，该分离株带有两个功能等位基因，用于强效可激活的Stx2变体毒素Stx2d，其中存在转化Stx2d的噬菌体。我们首先构建了产生一种或另一种Stx2d毒素的B2F1突变体，发现仅产生Stx2d1的突变体比产生Stx2d2的突变体产生的毒素更少。与该结果一致，在链霉素治疗的STEC感染小鼠模型中，产生Stx2d1的突变体减毒。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）治疗小鼠时，动物对产生Stx2d1的突变体更敏感。此外，从暴露于仅产生Stx2d1的突变体的裂解物中的菌株DH5α的噬菌斑中分离出了含有 stx 2d1 的溶菌原，并用当用丝裂霉素C诱导溶原时，编码RecA的质粒具有细胞毒性。最后，电子显微镜检查产生Stx2d1的突变体提取物的提取物显示出类似于原型Stx2转化噬菌体933W的六边形颗粒。这些观察结果在一起提供了有力的证据，证明Stx2d1的表达与噬菌体有关。我们得出结论，尽管B2F1中的 stx 2d1 -和 stx 2d2 -侧翼区域的序列相似，但Stx2d1在其毒素转化噬菌体的背景下表达被抑制，而Stx2d2表达则独立于噬菌体诱导。

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