Enterotoxigenic Escherichia coli (ETEC) can cause intestinal inflammation and diarrhea in yaks, which has a negative impact on their economic value. In recent years, probiotics have gained increasing attention as a pure, natural, nontoxic, harmless, and residue-free additive. However, the underlying mechanisms by which probiotics safeguard against ETEC are not completely elucidated. This study aimed to investigate the protective effect of Enterococcus faecium (E. faecium) against ETEC infection in mice through oral gavage. Morphological changes were examined through light microscopy. The expressions of inflammatory cytokines (IL-1β, IL-6, TNF-α, IL-10, NF-κB, and NLRP3), tight junction protein (ZO-1, Claudin-1), and pyroptosis (Caspase-1, Caspase-4, and gasdermin D (GSDMD)) were detected using immunohistochemistry and quantitative real-time PCR. The results indicate that ETEC infection triggers the activation of inflammation-related pathways (NF-κB) and NLRP3 inflammasome, leading to the expression of a large number of inflammatory cytokines. Additionally, the activation of NLRP3 leads to the release of GSDMD activation through Caspase-1, ultimately resulting in inflammatory injury and pyroptosis. Feeding mice E. faecium early resulted in an increase in the expression of tight junction protein, a reduction in inflammatory cytokines, and alleviation of inflammatory injury and pyroptosis in intestinal tissues. Our research indicates that E. faecium has the ability to antagonize ETEC and provide protection to the gastrointestinal mucosa in mice.
Keywords: Enterococcus faecium; Escherichia coli; gastrointestinal mucosa; inflammatory cytokines.