Prophage-encoded virulence factor, Gp05, contributes to endothelial cell dysfunction and immune evasion to promote persistent methicillin-resistant Staphylococcus aureus endovascular infections.

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of endovascular infections, where interactions with endothelial cells play a critical role in pathogenesis. Gp05, a prophage-encoded protein, has previously been implicated in promoting antibiotic persistence by modulating MRSA cellular physiology and evading neutrophil-mediated killing. In this study, we investigated the role of Gp05 in MRSA-endothelial cell interactions, focusing on its impact on bacterial adhesion, invasion, cytotoxicity, and the host inflammatory response. Using an isogenic MRSA strain set-including a clinical persistent bacteremia isolate (PB 300-169), a gp05 deletion mutant, and a gp05-complemented strain-we found that deletion of gp05 significantly impaired MRSA invasion, intracellular survival, and damage toward endothelial cells. Notably, endothelial cells infected with the gp05 deletion mutant induced a heightened endothelial inflammatory response, characterized by increased production of cytokines (IL-1β, TNF-α, IFN-γ, and CCL2/MCAF) and upregulated expression of inflammatory- and adhesion-associated molecules (VEGF, VCAM-1, TLR2, and TLR6). Furthermore, treatment of endothelial cells with purified Gp05 protein alone was sufficient to suppress endothelial inflammatory signaling and induce cytotoxic effects, suggesting that Gp05 exerts both intracellular and extracellular functions: intracellularly, by attenuating host immune activation to promote bacterial survival, and extracellularly, by directly disrupting endothelial barrier integrity and dampening immune recognition. In conclusion, Gp05 is a key virulence factor that contributes to MRSA persistence in endovascular infections by promoting endothelial cell dysfunction, suppressing host immune response, and enhancing bacterial survival. These findings highlight Gp05 as a potential therapeutic agent for disrupting MRSA pathogenesis in vascular tissues.

Importance: This study reveals the critical role of Gp05, a prophage-encoded protein, in promoting antibiotic persistence during MRSA endovascular infections by modulating endothelial cell responses. By demonstrating that Gp05 enhances S. aureus endothelial cell invasion, intracellular survival, and cytotoxicity, while simultaneously suppressing host immune signaling, the research highlights Gp05 as a dual-function factor with both intracellular and extracellular effects on MRSA-host endothelial cell interactions. The identification of Gp05's capacity to disrupt endothelial cells and dampen host immune system advances our understanding of the mechanism of MRSA persistence. Given the clinical challenges of treating persistent MRSA infections, especially in endovascular contexts, these findings position Gp05 as a compelling target for novel therapeutic strategies.