Instituto de Investigación de la Cadena Láctea IDICaL (INTA-CONICET), Rafaela, Argentina.
U.S Meat Animal Research Center, Agricultural Research Service, U.S. Department of Agriculture, Clay Center, Nebraska, United States of America.
PLoS One. 2021 Oct 28;16(10):e0258753. doi: 10.1371/journal.pone.0258753. eCollection 2021.
Cattle are the main reservoir of Enterohemorrhagic Escherichia coli (EHEC), with O157:H7 the distinctive serotype. EHEC is the main causative agent of a severe systemic disease, Hemolytic Uremic Syndrome (HUS). Argentina has the highest pediatric HUS incidence worldwide with 12-14 cases per 100,000 children. Herein, we assessed the genomes of EHEC O157:H7 isolates recovered from cattle in the humid Pampas of Argentina. According to phylogenetic studies, EHEC O157 can be divided into clades. Clade 8 strains that were classified as hypervirulent. Most of the strains of this clade have a Shiga toxin stx2a-stx2c genotype. To better understand the molecular bases related to virulence, pathogenicity and evolution of EHEC O157:H7, we performed a comparative genomic analysis of these isolates through whole genome sequencing. The isolates classified as clade 8 (four strains) and clade 6 (four strains) contained 13 to 16 lambdoid prophages per genome, and the observed variability of prophages was analysed. An inter strain comparison show that while some prophages are highly related and can be grouped into families, other are unique. Prophages encoding for stx2a were highly diverse, while those encoding for stx2c were conserved. A cluster of genes exclusively found in clade 8 contained 13 genes that mostly encoded for DNA binding proteins. In the studied strains, polymorphisms in Q antiterminator, the Q-stx2A intergenic region and the O and P γ alleles of prophage replication proteins are associated with different levels of Stx2a production. As expected, all strains had the pO157 plasmid that was highly conserved, although one strain displayed a transposon interruption in the protease EspP gene. This genomic analysis may contribute to the understanding of the genetic basis of the hypervirulence of EHEC O157:H7 strains circulating in Argentine cattle. This work aligns with other studies of O157 strain variation in other populations that shows key differences in Stx2a-encoding prophages.
牛是肠出血性大肠杆菌（EHEC）的主要宿主，其中 O157：H7 是其特征血清型。EHEC 是严重全身性疾病溶血性尿毒症综合征（HUS）的主要病原体。阿根廷的儿科 HUS 发病率居世界首位，每 10 万名儿童中有 12-14 例。在此，我们评估了从阿根廷湿润潘帕斯牛群中分离出的 EHEC O157:H7 分离株的基因组。根据系统发育研究，EHEC O157 可分为进化枝。被归类为高毒力的 8 号进化枝菌株。该进化枝的大多数菌株具有志贺毒素 stx2a-stx2c 基因型。为了更好地了解与 EHEC O157:H7 的毒力、致病性和进化相关的分子基础，我们通过全基因组测序对这些分离株进行了比较基因组分析。分类为 8 号进化枝（4 株）和 6 号进化枝（4 株）的分离株每个基因组含有 13 到 16 个 λ样噬菌体，分析了观察到的噬菌体变异性。菌株间比较表明，虽然一些噬菌体高度相关且可归为家族，但其他噬菌体则是独特的。编码 stx2a 的噬菌体高度多样化，而编码 stx2c 的噬菌体则保守。仅在 8 号进化枝中发现的基因簇包含 13 个基因，这些基因主要编码 DNA 结合蛋白。在所研究的菌株中，Q 终止子、Q-stx2A 基因间区和噬菌体复制蛋白 O 和 Pγ等位基因的多态性与 Stx2a 产生的不同水平相关。正如预期的那样，所有菌株都具有高度保守的 pO157 质粒，尽管一株菌的蛋白酶 EspP 基因中存在转座子中断。这项基因组分析可能有助于理解在阿根廷牛群中流行的 EHEC O157:H7 菌株的高毒力的遗传基础。这项工作与其他关于 O157 菌株在其他人群中的变异的研究一致，这些研究显示了编码 stx2a 的噬菌体在关键方面存在差异。
