Theaflavin Ameliorates Streptococcus suis -Induced Infection In Vitro and In Vivo

( ) is one of the most important zoonotic pathogens that threaten the lives of pigs and humans. Even worse, the increasingly severe antimicrobial resistance in is becoming a global issue. Therefore, there is an urgent need to discover novel antibacterial alternatives for the treatment of infection. In this study, we investigated theaflavin (TF1), a benzoaphenone compound extracted from black tea, as a potential phytochemical compound against . TF1 at MIC showed significant inhibitory effects on growth, hemolytic activity, and biofilm formation, and caused damage to cells in vitro. TF1 had no cytotoxicity and decreased adherent activity of to the epithelial cell Nptr. Furthermore, TF1 not only improved the survival rate of -infected mice but also reduced the bacterial load and the production of IL-6 and TNF-α. A hemolysis test revealed the direct interaction between TF1 and Sly, while molecular docking showed TF1 had a good binding activity with the Glu198, Lys190, Asp111, and Ser374 of Sly. Moreover, virulence-related genes were downregulated in the TF1-treated group. Collectively, our findings suggested that TF1 can be used as a potential inhibitor for treating infection in view of its antibacterial and antihemolytic activity.