Function analysis of LIPI-4 in <i>listeria monocytogenes</i> reveals a key role of flagella formation in the regulation of virulence

<i>Listeria</i> Pathogenicity Island 4 (LIPI-4), a newly discovered virulence gene cluster, plays a critical role in the development of central nervous system infections and maternal-foetal infections caused by <i>Listeria monocytogenes</i>. This study aimed to clarify the pathogenic role of LIPI-4 in <i>L. monocytogenes</i>. Our findings revealed that LIPI-4 is involved in the invasion and intracellular proliferation of <i>L. monocytogenes</i> in Caco-2, hCMEC/D3, HTR-8/Svneo, and RAW264.7 cells, and facilitates its intercellular migration. Further investigations demonstrated that the deletion of LIPI-4 significantly reduces bacterial motility and impairs flagellum formation. Transcriptomic analysis further indicated that LIPI-4 regulates flagellum formation by modulating microbial metabolic processes and carbon metabolism. Our research demonstrates that LIPI-4 promotes flagellum formation through metabolic regulation, thereby enhancing <i>L. monocytogenes</i> colonization and cellular invasion. This discovery provides novel insights into the pathogenic mechanisms of <i>L. monocytogenes</i>.