The Role of Internalin B Regulation and Variation in the Vertical Transmission of Listeria monocytogenes

Listeria monocytogenes (Lm) is a foodborne pathogen capable of causing severe infection during pregnancy. However, the bacterial strains most likely to cause vertical transmission remain understudied. This work investigates the increased placental and fetal invasion of Lm strain 07PF0776, which exhibits higher surface abundance of the virulence factor Internalin B (InlB) compared to the commonly studied strain 10403S. We identify a post-transcriptional regulatory mechanism involving the small RNA rliB, which reduces inlB expression in 10403S but not 07PF0776. Expanding our analysis to additional Lm strains, we observe a correlation between surface InlB abundance, vertical transmission rates, and rliB sequence variation, suggesting a broader role for inlAB regulation in Lm pathogenesis. In addition, structural polymorphisms in InlB influence its interactions with bacterial wall teichoic acids and host proteoglycans. These findings provide insights into the molecular determinants of pregnancy-associated listeriosis and inform strategies for surveillance and prevention of severe disease.