Inflammation, the kynurenines and mucosal injury during human experimental enterotoxigenic Escherichia coli infection

Enterotoxigenic Escherichia coli (ETEC) is an important cause of children’s and travelers’ diarrhea, especially in low- and middle-income countries. ETEC is a non-invasive gut pathogen, colonizing the small intestinal wall before secreting diarrhea-inducing enterotoxins. We sought to investigate the impact of ETEC infection on local and systemic host defenses by examining plasma markers of inflammation and mucosal injury, as well as kynurenine pathway metabolites.

Plasma from 21 volunteers experimentally infected with ETEC, were collected before and 1, 2, 3, and 7 days after ingesting the ETEC dose, grouped according to the level of intestinal ETEC proliferation: 14 volunteers experienced substantial proliferation (SP) and 7 had low proliferation (LP). Plasma markers of inflammation, kynurenine pathway metabolites, and related cofactors (vitamins B2 & B6) were quantified by using targeted mass spectrometry, while ELISA was used to quantify the mucosal injury markers Reg3a and iFABP.

We found increased concentrations of plasma C-reactive protein (CRP), serum amyloid A (SAA), neopterin, kynurenine/tryptophan ratio (KTR) and Reg3a in the SP group following dose ingestion. Vitamin B6 forms, pyridoxal 5'-phosphate and pyridoxal, and decreased over time in the SP group. CRP, SAA and the pyridoxic acid ratio correlated with ETEC proliferation levels.

The observed changes following experimental ETEC infection indicate that ETEC, despite causing a non-invasive infection, induced systemic inflammation and mucosal injury when proliferating substantially, even in cases without diarrheal symptoms. It is conceivable that ETEC infections, especially when repeated, contribute to the negative health impact on young children living in ETEC-endemic areas.

产肠毒素大肠杆菌（Enterotoxigenic Escherichia coli, ETEC）是引发儿童与旅行者腹泻的重要致病菌，在中低收入国家尤为高发。ETEC属于非侵袭性肠道病原菌，可定植于小肠壁并分泌致泻肠毒素。本研究旨在通过检测炎症与黏膜损伤的血浆标志物，以及犬尿氨酸通路代谢物，探究ETEC感染对宿主局部与全身防御系统的影响。

本研究收集了21名经实验感染ETEC的志愿者的血浆样本，采集时间点为摄入ETEC菌液前，以及摄入后1、2、3和7天；并按照肠道ETEC增殖水平分为两组：14名志愿者出现显著增殖（SP组），7名志愿者增殖水平较低（LP组）。研究采用靶向质谱法定量检测血浆炎症标志物、犬尿氨酸通路代谢物及相关辅因子（维生素B2与B6），同时通过酶联免疫吸附实验（Enzyme-Linked Immunosorbent Assay, ELISA）定量检测黏膜损伤标志物Reg3a与iFABP。

结果显示，摄入菌液后，SP组血浆C反应蛋白（C-reactive protein, CRP）、血清淀粉样蛋白A（serum amyloid A, SAA）、新蝶呤（neopterin）、犬尿氨酸/色氨酸比值（kynurenine/tryptophan ratio, KTR）及Reg3a的浓度均显著升高。SP组中维生素B6的两种形式——5'-磷酸吡哆醛（pyridoxal 5'-phosphate）与吡哆醛（pyridoxal）的水平随时间呈下降趋势。CRP、SAA及吡哆酸比值与ETEC增殖水平呈显著相关。

实验性ETEC感染后的上述变化表明，尽管ETEC引发的是非侵袭性感染，但当其发生显著增殖时，即使未出现腹泻症状，仍可诱导全身炎症反应与黏膜损伤。由此可以推测，ETEC感染（尤其是反复感染）会对ETEC流行区域的幼儿健康造成负面影响。