Selective Inhibition of Yersinia enterocolitica Type III Secretion by Lindera obtusiloba Extract and Cinnamtannin B1

<b>Background/Objectives</b>: Selective inhibition of bacterial virulence factors is a promising strategy to convert pathogenic bacteria into non-pathogenic commensals, circumventing the challenge of antibiotic resistance. This approach enables the host immune system to eliminate virulence-attenuated pathogens. <b>Methods</b>: In this study, we evaluated the effects of <i>Lindera obtusiloba</i> Blume extract and cinnamtannin B1, the active component of the ethyl acetate fraction, on the type III secretion system (T3SS) of <i>Yersinia enterocolitica</i>. <b>Results</b>: The ethyl acetate fraction, at 100 mg/L, effectively suppressed all three T3SS components-the flagellar, Ysa, and Ysc T3SSs. Cinnamtannin B1, isolated from the ethyl acetate fraction through separation and identified through nuclear magnetic resonance spectrometer analysis, significantly inhibited flagellar and Ysa T3SS secretion, while selectively inhibiting expression of key effector proteins YopH and YopO in the Ysc T3SS. Additionally, cinnamtannin B1 reduced <i>Y. enterocolitica</i>-induced RAW 264.7 macrophage mortality and prevented poly (ADP-ribose) polymerase degradation, a marker of apoptosis. <b>Conclusions</b>: These findings suggest cinnamtannin B1 from <i>L. obtusiloba</i> as a selective T3SS-targeting compound with mechanistic potential for anti-virulence intervention. Further in vivo validation will be necessary to evaluate its therapeutic applicability.