Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada.
Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, ON, Canada.
Microbiology (Reading). 2012 Sep;158(Pt 9):2399-2407. doi: 10.1099/mic.0.056374-0. Epub 2012 Jul 5.
Enterohaemorrhagic Escherichia coli (EHEC) survives exposure to acute acid stress during gastric passage and progresses to colonize the large intestine. We previously reported that acid stress significantly increases host adhesion of EHEC O157 : H7 and is associated with a coincident upregulation of the expression of a putative adhesin gene, yadK. Further gene expression analysis now confirms that yadK is minimally transcribed under unstressed conditions and is significantly upregulated under acid stress. Immunoblotting with an anti-YadK polyclonal antiserum demonstrates that YadK protein is also upregulated after acid stress. Disruption of yadK results in loss of the acid-induced adhesion increase seen for wild-type EHEC to human epithelial cells in vitro and complementation in trans fully restores the acid-induced adhesion phenotype to the wild-type level. Significantly, no difference is observed in adhesion of the unstressed yadK mutant relative to wild-type, indicating that YadK does not play a role in adhesion of unstressed EHEC. Anti-YadK antiserum inhibits the acid-induced adhesion enhancement of EHEC but has no effect on adhesion of unstressed EHEC. There is no significant difference in the viability of either the unstressed or the acid-stressed yadK mutant relative to the similarly treated wild-type, suggesting that yadK is not involved in acid tolerance. These results provide persuasive evidence that YadK plays a significant role in the adhesion of acid-stressed EHEC to epithelial cells, and support a role for acid stress as a factor which may regulate bacteria-host attachment and lead to increased EHEC colonization and virulence.
产志贺样毒素大肠杆菌（EHEC）能够在胃酸环境中存活并通过定殖大肠进行传播。我们之前的研究发现，酸应激显著增加了 EHEC O157:H7 对宿主的黏附作用，同时还导致一个假定黏附基因 yadK 的表达水平上调。进一步的基因表达分析证实，yadK 在未受应激的条件下转录水平很低，而在酸应激条件下表达量显著上调。用抗 YadK 多克隆抗血清进行免疫印迹分析表明，YadK 蛋白在酸应激后也会发生上调。yadK 缺失会导致 EHEC 野生型在体外对人上皮细胞的黏附增加，而酸诱导的黏附表型在转座互补后完全恢复到野生型水平。值得注意的是，yadK 突变株在未受应激时的黏附能力与野生型没有差异，这表明 YadK 并不参与 EHEC 未受应激时的黏附。抗 YadK 抗血清可抑制 EHEC 酸诱导的黏附增强，但对未受应激的 EHEC 黏附没有影响。与同样处理的野生型相比，yadK 突变株在未受应激或酸应激时的存活率没有显著差异，这表明 yadK 不参与酸耐受。这些结果提供了令人信服的证据，表明 YadK 在酸应激 EHEC 与上皮细胞黏附中发挥重要作用，并支持酸应激作为一种可能调节细菌-宿主附着并导致 EHEC 定植和毒力增加的因素的作用。
