| Summary: | <b>Background:</b> Although antibiotic therapy is currently a gold standard for bacterial infections, it is not used for severe diseases like enterohemorrhagic <i>Escherichia coli</i>, in which the Shiga toxin is overproduced by antibiotic action. The <i>Lonicera japonica</i> flower bud (LJF) is an herbal component used against purulent diseases in traditional Japanese and Chinese medicine. We investigated the effects of LJF extract (LJFE) on <i>Citrobacter rodentium</i>-induced digestive tract infection in a mouse model. <b>Methods:</b><i>Citrobacter rodentium</i> and LJFE were orally administered to C57BL/6 mice. The survival rate and bacterial colonization in the large intestine, mesenteric lymph node, and blood of mice were evaluated. Cytokines secreted from intraperitoneal macrophages of LJFE-treated mice were measured using ELISA. Moreover, the phagocytic activity of intraperitoneal macrophages against <i>Citrobacter rodentium</i> was compared between LJFE- or chlorogenic acid (CGA)-treated mice. <b>Results:</b> LJFE significantly increased the survival rate and decreased <i>Citrobacter rodentium</i> colonization in mice. Moreover, the values of tumor necrosis factor-α, interleukin-1β, and interferon-γ secreted from macrophages were increased following LJFE treatment. While macrophages of LJFE-treated mice showed a significant phagocytic activity, macrophages of CGA-treated mice only showed a phagocytic tendency. <b>Conclusions:</b> LJF may be useful for treating <i>Citrobacter rodentium</i>-induced digestive tract infection.
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