Comparative analysis of virulence in Listeria monocytogenes: Insights from genomic variations and in vitro cell-based studies.

Listeria monocytogenes is a significant foodborne pathogen capable of crossing the intestinal barrier and causing invasive listeriosis. This study focused on 37 L. monocytogenes strains isolated from food and clinical samples in the Shanghai region between 2020 and 2023. The in vitro cell models were used to assess the bacteria's ability to cross the intestinal barrier, as well as their adhesion and invasion capabilities in placental cells. Whole-genome analysis of the bacterial strains was also performed. The results showed that strains from lineage I exhibited significantly higher translocation ability across the Caco-2 barrier, as well as higher adhesion and invasion rates in JEG-3 cells, compared to strains from lineage II. Strains from serogroup IIb demonstrated significantly higher adhesion and invasion rates in JEG-3 cells than those from serogroups IIa and IIc. Clinical isolates had significantly higher translocation ability across the Caco-2 barrier, and higher adhesion and invasion rates in JEG-3 cells, compared to food-derived strains. Mutations in the inlA gene were detected in ST9 and ST121 strains, which may be a potential cause of the reduced virulence observed in these ST types. The presence of LIPI-4 in ST87 strains and LIPI-3 in ST3 strains may also explain the high virulence of these ST types strains. The results of this study, by integrating in vitro virulence phenotypes with genomic data, further enhance the understanding of virulence differences among different bacterial strains.