A Family of Indoles Regulate Virulence and Shiga Toxin Production in Pathogenic E. coli

Enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC) and enteroaggregative E. coli (EAEC) are intestinal pathogens that cause food and water-borne disease in humans. Using biochemical methods and NMR-based comparative metabolomics in conjunction with the nematode Caenorhabditis elegans, we developed a bioassay to identify secreted small molecules produced by these pathogens. We identified indole, indole-3-carboxaldehyde (ICA), and indole-3-acetic acid (IAA), as factors that only in combination are sufficient to kill C. elegans. Importantly, although lethal to C. elegans, these molecules downregulate several bacterial processes important for pathogenesis in mammals. These include motility, biofilm formation and production of Shiga toxins. Some pathogenic E. coli strains are known to contain a Locus of Enterocyte Effacement (LEE), which encodes virulence factors that cause “attaching and effacing” (A/E) lesions in mammals, including formation of actin pedestals. We found that these indole derivatives also downregulate production of LEE virulence factors and inhibit pedestal formation on mammalian cells. Finally, upon oral administration, ICA inhibited virulence and promoted survival in a lethal mouse infection model. In summary, the C. elegans model in conjunction with metabolomics has facilitated identification of a family of indole derivatives that broadly regulate physiology in E. coli, and virulence in pathogenic strains. These molecules may enable development of new therapeutics that interfere with bacterial small-molecule signaling.

肠致病性大肠杆菌（Enteropathogenic Escherichia coli, EPEC）、肠出血性大肠杆菌（Enterohemorrhagic Escherichia coli, EHEC）与肠聚集性大肠杆菌（Enteroaggregative Escherichia coli, EAEC）均为可引发人类食源性及水源性疾病的肠道致病菌。本研究结合生化方法、基于核磁共振（Nuclear Magnetic Resonance, NMR）的比较代谢组学技术，以及秀丽隐杆线虫（Caenorhabditis elegans）模型，开发了一种生物测定方法，用于鉴定此类致病菌分泌的小分子物质。我们成功鉴定出吲哚（indole）、吲哚-3-甲醛（Indole-3-carboxaldehyde, ICA）以及吲哚-3-乙酸（Indole-3-acetic acid, IAA），仅需三者联合即可致死秀丽隐杆线虫。

重要的是，尽管此类物质对秀丽隐杆线虫具有致死活性，但它们可下调多种与哺乳动物致病相关的关键细菌生理过程，包括细菌运动能力、生物被膜形成以及志贺毒素（Shiga toxins）的产生。部分致病性大肠杆菌菌株携带肠细胞脱落位点（Locus of Enterocyte Effacement, LEE），该位点编码可在哺乳动物体内引发“黏附脱落（attaching and effacing, A/E）”损伤（包括肌动蛋白基座形成）的毒力因子。我们发现，此类吲哚衍生物同样可下调LEE编码的毒力因子表达，并抑制哺乳动物细胞表面的肌动蛋白基座形成。

最终实验证实，经口服给药后，ICA可在致死性小鼠感染模型中抑制致病菌毒力并提升小鼠存活率。综上，结合代谢组学技术的秀丽隐杆线虫模型助力我们鉴定出一类吲哚衍生物，该类物质可广泛调控大肠杆菌的生理功能与致病菌株的毒力，有望为开发靶向干预细菌小分子信号通路的新型治疗策略提供新方向。