Impact of Gene Network Alterations Induced by Deletion of Key Virulence Factors in ST87 Listeria monocytogenes on Placental Infection

Listeria monocytogenes is a globally recognized foodborne pathogen. The ST87 L. monocytogenes strains have become the most prevalent clinical isolates in China and are closely associated with perinatal listeriosis. This study aims to investigate the essential roles of key virulence factors in the L. monocytogenes ST87 strain during placental infection, focusing on the clinically isolated epidemic ST87 strain from China and constructing gene deletion mutants of inlA, hly, inlP, and actA. The roles of these genes in placental infection were systematically investigated using 2D and 3D trophoblast cell models (HTR‑8/SVneo, JEG‑3), non‑pregnant and pregnant ICR mice, and transcriptomic analysis. The results showed that the Δhly mutant strain completely lost its virulence in mice models but showed a tendency of enhanced virulence in cell models; the ΔactA strain mutant exhibited reduced virulence in both animal models and placental cell models; the ΔinlA mutant strain displayed no significant change in virulence in animal models, yet its adhesion and invasion abilities decreased in cell models; the ΔinlP mutant strain only reduced the bacterial load in fetuses. By combining transcriptomic analysis with virulence phenotype analysis, it was found that the placental infection by ST87 L. monocytogenes depends on the synergistic effect of hly and actA, while inlA and inlP play auxiliary roles in the adhesion process. In addition, transcriptomic analysis identified potential genes associated with key virulence determinants of ST87 L. monocytogenes, including lytic polysaccharide monooxygenase, a MucBP domain-containing protein, and the alcohol dehydrogenase PduQ. This study provides a theoretical basis for elucidating the mechanism of gestational infection by the ST87 strain of L. monocytogenes and formulating intervention strategies.