Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Albany, California.
Foodborne Toxin Prevention and Detection Unit, Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Albany, California.
Foodborne Pathog Dis. 2020 Sep;17(9):555-567. doi: 10.1089/fpd.2019.2767. Epub 2020 Mar 4.
Shiga toxin-producing (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 (s) 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 ; whereas prophage 9 carried one set of . 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 promoters in RM10809-C3, including deletion of the late promoter and the mutations in , the binding site of antitermination protein Q. In contrast, both and within the promoter of 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 coding regions but also their regulatory factors are important in STEC risk assessment.
产志贺毒素（STEC）由一组在遗传构成和致病潜力方面差异很大的不同菌株组成。在这里，我们研究了在加利福尼亚州一个绿叶蔬菜种植区附近从牛粪便中分离出的一株携带多种志贺毒素基因（s）的牛源分离株在接触几种常用于食用动物的抗生素后产生志贺毒素（Stxs）的情况。RM10809-C3 菌株与一株 STEC O145:H28 菌株一起从加利福尼亚州一个绿叶蔬菜种植区附近的牛粪便中分离出来。RM10809-C3 的基因组由一个 5128479bp 的染色体和一个 122641bp 的质粒组成，编码 5108 个编码序列。RM10809-C3 株属于 O22:H8 血清型，使用多位序列型或核心基因组系统发育分析，与两株 STEC O168:H8 食品分离株聚类在一起。在 RM10809-C3 的基因组中鉴定出六个完整的前噬菌体，其中前噬菌体 4 包含两组；而前噬菌体 9 携带一组。在接触丝裂霉素 C 和恩诺沙星后，RM10809-C3 中检测到 Stx1 的产量增加，但接触四环素的细胞中未检测到 Stx2。相比之下，在用所检查的任何抗生素处理的细胞中都未检测到 Stx2。比较 RM10809-C3 菌株和 EDL933 菌株中的 Stx 转化前噬菌体发现，在 RM10809-C3 中，包括晚期启动子和终止蛋白 Q 结合位点的突变在内的 启动子发生了改变。相比之下，RM10809-C3 中 启动子内的 和 与 EDL933 中的相应启动子相同。此外，RM10809-C3 中 Stx1 噬菌体编码的蛋白 Q 与 EDL933 中的两个蛋白 Q 中的任意一个都具有 >94%的同一性；而 RM10809-C3 中 Stx2 噬菌体编码的两个蛋白 Q 都与 EDL933 中的任何一个蛋白 Q 都没有关系。RM10809-C3 中 Stx2 产生的自然沉默强调了不仅是 Stx2 编码区，而且它们的调控因子在 STEC 风险评估中都很重要。
