Söderlund Robert, Hurel Julie, Jinnerot Tomas, Sekse Camilla, Aspán Anna, Eriksson Erik, Bongcam-Rudloff Erik
SLU Global Bioinformatics Centre, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden.
Department of Microbiology, National Veterinary Institute (SVA), Uppsala, Sweden;
Infect Ecol Epidemiol. 2016 Feb 16;6:30246. doi: 10.3402/iee.v6.30246. eCollection 2016.
Escherichia coli O103:H2 occurs as verotoxigenic E. coli (VTEC) carrying only vtx 1 or vtx 2 or both variants, but also as vtx-negative atypical enteropathogenic E. coli (aEPEC). The majority of E. coli O103:H2 identified from cases of human disease are caused by the VTEC form. If aEPEC strains frequently acquire verotoxin genes and become VTEC, they must be considered a significant public health concern. In this study, we have characterized and compared aEPEC and VTEC isolates of E. coli O103:H2 from Swedish cattle.
Fourteen isolates of E. coli O103:H2 with and without verotoxin genes were collected from samples of cattle feces taken during a nationwide cattle prevalence study 2011-2012. Isolates were sequenced with a 2×100 bp setup on a HiSeq2500 instrument producing >100× coverage per isolate. Single-nucleotide polymorphism (SNP) typing was performed using the genome analysis tool kit (GATK). Virulence genes and other regions of interest were detected. Susceptibility to transduction by two verotoxin-encoding phages was investigated for one representative aEPEC O103:H2 isolate.
This study shows that aEPEC O103:H2 is more commonly found (64%) than VTEC O103:H2 (36%) in the Swedish cattle reservoir. The only verotoxin gene variant identified was vtx 1a . Phylogenetic comparison by SNP analysis indicates that while certain subgroups of aEPEC and VTEC are closely related and have otherwise near identical virulence gene repertoires, they belong to separate lineages. This indicates that the uptake or loss of verotoxin genes is a rare event in the natural cattle environment of these bacteria. However, a representative of a VTEC-like aEPEC O103:H2 subgroup could be stably lysogenized by a vtx-encoding phage in vitro.
大肠杆菌O103:H2可作为仅携带vtx 1或vtx 2或两种变体的产志贺毒素大肠杆菌（VTEC）出现，也可作为vtx阴性的非典型肠致病性大肠杆菌（aEPEC）出现。从人类疾病病例中鉴定出的大多数大肠杆菌O103:H2是由VTEC形式引起的。如果aEPEC菌株频繁获得志贺毒素基因并变成VTEC，那么它们必须被视为一个重大的公共卫生问题。在本研究中，我们对来自瑞典牛的大肠杆菌O103:H2的aEPEC和VTEC分离株进行了特征分析和比较。
在2011 - 2012年全国牛流行率研究期间，从牛粪便样本中收集了14株有无志贺毒素基因的大肠杆菌O103:H2分离株。在HiSeq2500仪器上以2×100 bp设置对分离株进行测序，每个分离株的覆盖率>100倍。使用基因组分析工具包（GATK）进行单核苷酸多态性（SNP）分型。检测毒力基因和其他感兴趣的区域。对一株代表性的aEPEC O103:H2分离株研究了其对两种编码志贺毒素的噬菌体转导的敏感性。
本研究表明，在瑞典牛群中，aEPEC O103:H2比VTEC O103:H2更常见（64%比36%）。鉴定出的唯一志贺毒素基因变体是vtx 1a。通过SNP分析进行的系统发育比较表明，虽然aEPEC和VTEC的某些亚群密切相关且毒力基因库几乎相同，但它们属于不同的谱系。这表明在这些细菌的天然牛环境中，志贺毒素基因的获取或丢失是一个罕见事件。然而，一个类似VTEC的aEPEC O103:H2亚群的代表在体外可被编码vtx的噬菌体稳定溶原化。
