Highly conserved type 1 pili promote enterotoxigenic E. coli pathogen-host interactions

Enterotoxigenic Escherichia coli (ETEC), defined by their elaboration of heat-labile (LT) and/or heat-stable (ST) enterotoxins, are a common cause of diarrheal illness in developing countries. Efficient delivery of these toxins requires ETEC to engage target host enterocytes. This engagement is accomplished using a variety of pathovar-specific and conserved E. coli adhesin molecules as well as plasmid encoded colonization factors. Some of these adhesins undergo significant transcriptional modulation as ETEC encounter intestinal epithelia, perhaps suggesting that they cooperatively facilitate interaction with the host. Among genes significantly upregulated on cell contact are those encoding type 1 pili. We therefore investigated the role played by these pili in facilitating ETEC adhesion, and toxin delivery to model intestinal epithelia. We demonstrate that type 1 pili, encoded in the E. coli core genome, play an essential role in ETEC virulence, acting in concert with plasmid-encoded pathovar specific colonization factor (CF) fimbriae to promote optimal bacterial adhesion to cultured intestinal epithelium (CIE) and to epithelial monolayers differentiated from human small intestinal stem cells. Type 1 pili are tipped with the FimH adhesin which recognizes mannose with stereochemical specificity. Thus, enhanced production of highly mannosylated proteins on intestinal epithelia promoted FimH-mediated ETEC adhesion, while conversely, interruption of FimH lectin-epithelial interactions with soluble mannose, anti-FimH antibodies or mutagenesis of fimH effectively blocked ETEC adhesion. Moreover, fimH mutants were significantly impaired in delivery of both heat-stable and heat-labile toxins to the target epithelial cells in vitro, and these mutants were substantially less virulent in rabbit ileal loop assays, a classical model of ETEC pathogenesis. Collectively, our data suggest that these highly conserved pili play an essential role in virulence of these diverse pathogens.产肠毒素大肠杆菌（Enterotoxigenic Escherichia coli, ETEC）以分泌不耐热（heat-labile, LT）和/或耐热（heat-stable, ST）肠毒素为特征，是发展中国家腹泻疾病的常见致病菌。这类毒素的有效递送需要ETEC靶向结合宿主肠上皮细胞。这一结合过程可通过多种致病型特异性及保守的大肠杆菌黏附素分子，以及质粒编码的定植因子完成。当ETEC接触肠道上皮时，部分这类黏附素会发生显著的转录调控，这或许提示它们协同促进了病原菌与宿主的相互作用。在细胞接触后显著上调的基因中，包含编码1型菌毛（type 1 pili）的基因。因此，我们研究了这类菌毛在促进ETEC黏附以及向模型肠道上皮递送毒素中所发挥的作用。我们证实，由大肠杆菌核心基因组编码的1型菌毛在ETEC致病过程中发挥关键作用：它们与质粒编码的致病型特异性定植因子（colonization factor, CF）菌毛协同作用，可促进细菌与培养肠道上皮细胞（cultured intestinal epithelium, CIE）以及由人类小肠干细胞分化形成的上皮单层的最优黏附。1型菌毛的顶端带有FimH黏附素，该黏附素具有立体化学特异性识别甘露糖的能力。因此，肠道上皮细胞表面高度甘露糖基化蛋白的表达增强可促进FimH介导的ETEC黏附；反之，通过可溶性甘露糖、抗FimH抗体或对fimH基因进行诱变以阻断FimH凝集素-上皮相互作用，可有效抑制ETEC的黏附。此外，体外实验中，fimH突变株向靶上皮细胞递送耐热肠毒素与不耐热肠毒素的能力均显著受损，且这类突变株在经典ETEC致病模型——兔回肠袢试验中的致病力也大幅降低。综上，本研究数据表明，这类高度保守的菌毛在这类多样化病原菌的致病过程中发挥着不可或缺的作用。