Amyloid curli fibrils produced by Escherichia coli are well-known virulence factor influencing E. coli adhesion and biofilm formation. However, the impact of curli on intestinal epithelial barrier stimulated with proinflammatory cytokines is unknown. In the study, we examined the effect of curli produced by nonpathogenic E. coli K-12 and wild-type E. coli EC32 strains, and purified CsgA proteins on differentiated Caco-2 cell monolayers stimulated with a mixture of IL-1β, TNF-α, and INFγ cytokines as a model of ‘inflamed intestinal epithelial barrier’ in vitro. The results of the study indicated that curliated E. coli adhered better to polarized Caco-2 cells than their curli-deficient mutants and the adherence was further augmented by stimulation of epithelial cells with proinflammatory cytokines. Interestingly, curli reduced internalization but enhanced intracellular survival of the wild-type E. coli strain EC32 within intestinal epithelial cells. Curli-expressing E. coli, as well as purified CsgA proteins, attenuated IL-8 secretion by unstimulated Caco-2 cells, although the effect was barely observed on cytokine-stimulated cells. The findings of the study revealed that curli fibrils are an important virulence factor enabling curliated E. coli to effectively colonize intestinal epithelium especially in individuals with inflammatory intestinal disorders.

大肠杆菌产生的淀粉样卷曲原纤维是众所周知的影响大肠杆菌黏附和生物膜形成的毒力因子。然而，卷曲素对促炎细胞因子刺激的肠上皮屏障的影响尚不清楚。在这项研究中，我们检查了非致病性大肠杆菌K-12和野生型大肠杆菌EC32菌株产生的卷曲物，以及纯化的CsgA蛋白对IL-1β，TNF混合物刺激的分化Caco-2细胞单层的影响-α和INFγ细胞因子作为体外“发炎的肠上皮屏障”的模型。研究结果表明，卷曲的大肠杆菌与卷曲的缺陷型突变体相比，对极化的Caco-2细胞的粘附更好，并且通过促炎细胞因子刺激上皮细胞进一步增强了粘附。有趣的是，curli减少了内在化，但提高了肠道上皮细胞中野生型大肠杆菌EC32的细胞内存活率。表达卷曲的大肠杆菌以及纯化的CsgA蛋白减弱了未经刺激的Caco-2细胞的IL-8分泌，尽管对细胞因子刺激的细胞几乎没有观察到这种作用。该研究的发现表明，卷曲的原纤维是一种重要的致病因子，能够使卷曲的大肠杆菌有效地定居在肠道上皮中，特别是在患有炎症性肠道疾病的个体中。