Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major health threat with limited therapeutic options. We identified cucurbitacin B (CuB), a plant-derived triterpenoid, as a concurrent, complementary adjunct that attenuates bacterial virulence while modulating host responses. Structure-guided docking together with electrophoretic mobility shift assay (EMSA) and lysate-based cellular thermal shift assay (CETSA) supported the engagement of the Staphylococcus exoprotein expression protein response regulator (SaeR) at the α4/β5 pocket, lowering SaeR-regulated toxins and immune responses factors at nonbactericidal exposures. In cell models, CuB improved intracellular bacterial control, alleviated MRSA-induced oxidative stress, restored the mitochondrial membrane potential, and shifted macrophages toward an anti-inflammatory, M2-like phenotype consistent with nuclear factor kappaB (NF-κB) modulation. Drug-pairing studies revealed class-selective, concentration-dependent synergy with glycopeptides (vancomycin (Van) and dalbavancin) and additivity with linezolid, indicating complementation rather than broad sensitization. Under repeated sub-minimum inhibitory concentration (MIC) exposure across forty passages, CuB alone maintained a stable MIC, whereas CuB combined with Van attenuated Van resistance trajectories; head-to-head competition between passage-zero and passage-forty lineages revealed no fitness advantage after passaging with CuB. In murine peritonitis, catheter-associated biofilm, and infected wound models, CuB lowered the bacterial burden, reduced inflammatory injury, and facilitated wound closure by controlling infection and inflammation, and tissue immunofluorescence via CD86 and CD206 provided spatial corroboration. On-target support came from the minimal incremental benefit of CuB in infections caused by a SaeR-deficient strain. Together, these findings position CuB as a SaeR-focused antivirulence-immunomodulatory adjunct that complements Van