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Abstract Bacterial extracellular vesicles (BEVs) are nano‐size particles secreted by bacteria that carry various bioactive components. These vesicles are thought to provide a new window into the mechanisms by which bacteria affect their hosts, but their fundamental proprieties within human remain poorly understood. Here, we developed a single‐vesicle analytical platform that enabled BEV detection in complex biological samples of host. Using this platform, we found the presence of BEVs in the host circulation and they were mainly derived from gut microbes. We showed that the levels of circulating BEVs in humans significantly increased with aging due to an age‐related increase in intestinal permeability. Significantly different levels of BEVs in blood were also found in patients with colorectal cancer and colitis. Together, our study provides new insights into circulating BEV biology and reveals their potential as a new class of biomarkers.

Abstract Preeclampsia (PE) is a multisystem disorder with high maternal morbidity and mortality rates. Currently, no practical therapeutic approach is available to prevent PE progression, except for early delivery. Gut dysbiosis is associated with PE development. Previous data showed that the abundance of Akkermansia muciniphila (Am) was lower in patients with PE than in normotensive pregnant women. Here, in this study, decreased abundance of Am was observed in a PE mouse model. Also, we found that administration with Am could significantly attenuate systolic blood pressure, promote foetal growth and improve the placental pathology in mice with PE. Moreover, Am‐derived extracellular vesicles (AmEVs) were transferred from the gastrointestinal (GI) tract to the placenta and mitigated pre‐eclamptic symptoms in PE mice. These beneficial effects of AmEVs were mediated by enhanced trophoblast invasion of the spiral artery (SpA) and SpA remodelling through activation of the epidermal growth factor receptor (EGFR)–phosphatidylinositol‐3‐kinase (PI3K)–protein kinase B (AKT) signalling pathway. Collectively, our findings revealed the potential benefit of using AmEVs for PE treatment and highlighted important host–microbiota interactions.