Hemolysin III drives neuroinvasion and meningitis while impacting desiccation resilience in .

Unlabelled: is an emerging pathogen associated with severe neonatal diseases, including meningitis. Its ability to cross the blood-brain barrier (BBB) is critical for meningitis development, yet the underlying mechanisms remain unclear. This study investigates the role of Hemolysin III (Hly III), encoded by the , in neuroinvasion and environmental resilience. A markerless deletion of (Δ) revealed that the mutant exhibited unaltered biofilm formation, increased hydrophilicity, and enhanced desiccation resistance compared to the wild type, suggesting that Hly III imposes a fitness cost on under non-invasive conditions. In a rat infection model, the Δ strain demonstrated significantly reduced brain colonization without affecting bacterial loads in blood, liver, or spleen, underscoring the specific importance of Hly III in neuroinvasion. Cellular assays further revealed that, although the mutant maintained similar levels of adherence and invasion in Caco-2 cells and comparable adhesion to human brain microvascular endothelial cells (HBMECs) as the wild type, its ability to invade HBMECs was markedly diminished. These results suggest that Hly III is crucial for efficient neuroinvasion and BBB translocation while imposing a trade-off on environmental resilience, providing insights into the balance between virulence, and environmental adaptability in .

Importance: The ability of to cause severe neonatal infections, particularly meningitis, presents a significant public health concern, yet the molecular mechanisms that enable its neuroinvasion remain poorly understood. In this study, we identify Hemolysin III (Hly III), encoded by the ESA_00432 gene, as a key factor in the bacterium's ability to cross the blood-brain barrier (BBB) and initiate meningitis. Our findings demonstrate that Hly III is essential for efficient invasion of human brain microvascular endothelial cells (HBMECs) and subsequent brain colonization in a rat model, underscoring its critical role in neurotropism. Furthermore, we show that the absence of Hly III results in enhanced environmental resilience, as indicated by increased desiccation resistance and hydrophilicity. This metabolic trade-off between virulence and environmental adaptability reveals a novel aspect of 's pathogenesis and survival strategies. These insights open new avenues for developing targeted interventions to prevent neonatal meningitis and enhance food safety measures against this opportunistic pathogen.