Diosmetin targets sortase A to inhibit biofilm formation and combines with vancomycin against MRSA-induced pneumonia.

The global challenge of methicillin-resistant Staphylococcus aureus (MRSA) has driven the development of anti-virulence strategies. Sortase A (SrtA), a key enzyme responsible for anchoring surface virulence factors in MRSA, represents a promising target to overcome the limitations of conventional antibiotics. This study investigated the therapeutic potential and anti-virulence activity of diosmetin against Staphylococcus aureus (S. aureus). In a mouse model of S. aureus-induced pneumonia, diosmetin combined with vancomycin significantly improved therapeutic efficacy, as evidenced by increased survival, reduced pulmonary bacterial burden, and attenuated histopathological injury. In vitro, diosmetin exhibited no direct antibacterial activity at concentrations up to 512 μg/mL, yet it potentiated the antibacterial effect of vancomycin, with a checkerboard assay yielding a fractional inhibitory concentration index (FICI) of 0.375. Diosmetin disrupted the early stages of biofilm development by impairing sliding motility, reducing exopolysaccharide (EPS) production, and inhibiting bacterial adhesion. Molecular docking identified SrtA as a potential target. Surface plasmon resonance (SPR) and point mutation assays further confirmed the direct interaction between diosmetin and SrtA. Meanwhile, the fluorescence resonance energy transfer (FRET) assay demonstrated that diosmetin inhibited SrtA activity, with an IC50 of 9.28 μg/mL. Functional assays using the ΔsrtA mutant further supported the critical role of SrtA in mediating diosmetin's anti-virulence effects. Additionally, diosmetin protected A549 cells against S. aureus-induced pyroptosis and provided protection in a Galleria mellonella (G. mellonella) infection model. Collectively, diosmetin represents a promising anti-virulence agent targeting SrtA-associated biofilm formation and an antibiotic adjuvant for vancomycin against MRSA pneumonia.