Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Lethbridge, AB T1J 3Z4, Canada.
Appl Environ Microbiol. 2010 Jan;76(2):474-82. doi: 10.1128/AEM.01288-09. Epub 2009 Nov 30.
Escherichia coli O157:H7 strains fall into three major genetic lineages that differ in their distribution among humans and cattle. Several recent studies have reported differences in the expression of virulence factors between E. coli O157:H7 strains from these two host species. In this study, we wished to determine if important virulence-associated "mobile genetic elements" such as Shiga toxin 2 (Stx2)-encoding prophage are lineage restricted or are host source related and acquired independently of the pathogen genotype. DNA sequencing of the stx(2) flanking region from a lineage II (LII) strain, EC970520, revealed that the transcriptional activator gene Q in LI strain EDL933 (upstream of stx(2)) is replaced by a pphA (serine/threonine phosphatase) homologue and an altered Q gene in this and all other LII strains tested. In addition, nearly all LI strains carried stx(2), whereas all LII strains carried variant stx(2c) and 4 of 14 LI/II strains had copies of both stx(2) and variant stx(2c). Real-time PCR (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) demonstrated that LI and LI/II strains produce significantly more stx(2) mRNA and Stx2 than LII strains. However, among LI strains significantly more Stx2 is also produced by strains from humans than from cattle. Therefore, lineage-associated differences among E. coli O157:H7 strains such as prophage content, toxin type, and toxin expression may contribute to host isolation bias. However, the level of Stx2 production alone may also play an important role in the within-lineage association of E. coli O157:H7 strains with human clinical disease.
大肠杆菌 O157:H7 菌株分为三大遗传谱系，它们在人类和牛中的分布不同。最近的几项研究报告称，来自这两种宿主的大肠杆菌 O157:H7 菌株在毒力因子的表达上存在差异。在这项研究中，我们希望确定重要的与毒力相关的“可移动遗传元件”，如志贺毒素 2（Stx2）编码的噬菌体是否受到谱系限制，或者与宿主来源有关，并独立于病原体基因型获得。对谱系 II（LII）菌株 EC970520 的 stx(2)侧翼区域进行 DNA 测序显示，LI 菌株 EDL933（stx(2)上游）的转录激活基因 Q 被一个 pphA（丝氨酸/苏氨酸磷酸酶）同源物和该基因的一个改变的基因所取代，而且在所有测试的 LII 菌株中均如此。此外，几乎所有的 LI 菌株都携带 stx(2)，而所有的 LII 菌株都携带变体 stx(2c)，在 14 株 LI/II 菌株中有 4 株携带 stx(2)和变体 stx(2c)的拷贝。实时 PCR（RT-PCR）和酶联免疫吸附试验（ELISA）表明，LI 和 LI/II 菌株产生的 stx(2) mRNA 和 Stx2 明显多于 LII 菌株。然而，在 LI 菌株中，来自人类的菌株产生的 Stx2 也明显多于来自牛的菌株。因此，大肠杆菌 O157:H7 菌株之间的谱系相关差异，如噬菌体含量、毒素类型和毒素表达，可能导致宿主分离偏倚。然而，Stx2 产生水平本身也可能在大肠杆菌 O157:H7 菌株与人类临床疾病的谱系内关联中发挥重要作用。
