Shiga toxin-producing Escherichia coli (STEC) consists of a group of diverse strains differing greatly in genetic make-up and pathogenicity potential. Here, we investigated production of Shiga toxins (Stxs) in a bovine isolate carrying multiple Shiga toxin genes (stxs) after exposure to several antibiotics commonly used in food animals. Strain RM10809-C3 was co-isolated with a STEC O145:H28 strain from cattle feces near a leafy greens-growing region in California. The genome of RM10809-C3 is composed of a 5,128,479-bp chromosome and a 122,641-bp plasmid, encoding 5108 coding sequences. Strain RM10809-C3 belongs to serotype O22:H8 and is clustered together with two STEC O168:H8 food isolates using either multilocus sequence type or core genome-based phylogenetic analysis. Six intact prophages were identified in the genome of RM10809-C3, among which prophage 4 contained two sets of stx_2d; whereas prophage 9 carried one set of stx_1a. Increased production of Stx1 was detected in RM10809-C3 after exposure to mitomycin C and enrofloxacin, but not in cells exposed to tetracycline. In contrast, Stx2 remained undetectable in cells treated with any of the antibiotics examined. Comparison of Stx-converting prophages in strain RM10809-C3 with those in strain EDL933 revealed altered stx2 promoters in RM10809-C3, including deletion of the late promoter P_R′ and the mutations in qut, the binding site of antitermination protein Q. In contrast, both P_R′ and qut within the promoter of stx1 in RM10809-C3 were identical to the corresponding one in EDL933. Further, the protein Q encoded by Stx1-prophage in RM10809-C3 exhibited >94% identity with either of the two EDL933 protein Q; whereas both protein Q encoded by Stx2-prophage in RM10809-C3 were distantly related to any of the EDL933 protein Q. Natural silence of Stx2 production in strain RM10809-C3 emphasizes that not only the stx coding regions but also their regulatory factors are important in STEC risk assessment.

中文翻译：

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对产生志贺毒素 1 的环境大肠杆菌菌株中志贺毒素 2 自然灭活的基因组洞察。

产志贺毒素大肠杆菌(STEC) 由一组在基因组成和致病潜力方面差异很大的不同菌株组成。这里，我们调查生产志贺毒素（Stxs）在牛分离物携带多个志贺毒素基因（STXs) 接触食用动物常用的几种抗生素后。菌株 RM10809-C3 与来自加利福尼亚绿叶蔬菜种植区附近牛粪的 STEC O145:H28 菌株共同分离。RM10809-C3 的基因组由 5,128,479-bp 染色体和 122,641-bp 质粒组成，编码 5108 个编码序列。菌株 RM10809-C3 属于血清型 O22:H8，并使用多位点序列类型或基于核心基因组的系统发育分析与两个 STEC O168:H8 食品分离株聚集在一起。RM10809-C3基因组中鉴定出6个完整的原噬菌体，其中原噬菌体4含有两组stx _2d；而 prophage 9 携带一组stx _1a. 在暴露于丝裂霉素 C 和恩诺沙星后，在 RM10809-C3 中检测到 Stx1 的产生增加，但在暴露于四环素的细胞中未检测到。相比之下，Stx2 在用任何检测的抗生素处理的细胞中仍然检测不到。比较STX-转换在应变RM10809-C3原噬菌体与在应变EDL933显示改变的STX2中RM10809-C3启动子，包括晚期启动子的缺失P _R'和在突变QUT，抗终止蛋白Q的结合位点与此相反, stx1启动子内的P _R'和qutRM10809-C3 中的与 EDL933 中的对应相同。此外，由 RM10809-C3 中 Stx1-原噬菌体编码的蛋白 Q 与两种 EDL933 蛋白 Q 中的任何一种表现出 >94% 的同一性；而在RM10809-C3通过将Stx2，原噬菌体编码的蛋白都被Q远亲任何应变的Stx2生产EDL933蛋白Q.自然沉默的RM10809-C3强调，不仅是STX编码区，而且其监管的因素是很重要的STEC 风险评估。