Repurposing Diflunisal as an Antivirulence Agent Against Staphylococcus aureus

Infections refractory to standard antibiotic therapy are contributing to adverse treatment outcomes in patients suffering from deep-seated bacterial infections caused by increasingly resistant pathogens. Adjunctive strategies targeting bacterial virulence factors have been considered to supplement the host immune response in fighting the infection. Previous studies suggest that the FDA-approved anti-inflammatory drug diflunisal inhibits Staphylococcus aureus (SA) α-toxin expression by its interaction with the response regulator AgrA. We investigated the broader anti-virulence properties of diflunisal against pathogenic strains of SA and established proof-of-concept for its efficacy in blocking SA virulence. Our studies reveal that diflunisal inhibits α-toxin production, sensitizes SA to cationic antibiotics and human antimicrobial peptides, inhibits the production of the golden pigment staphyloxanthin, and reduces biofilm formation. Molecular docking simulations revealed potential interactions between diflunisal and AgrA binding sites. In addition, sequence alignment of the SA AgrA response regulator demonstrated similarities to other response regulators involved in controlling virulence factor expression. Appreciation of the antivirulence properties of diflunisal supports a therapeutic strategy distinct from structurally similar compounds, such as salicylic acid. The repurposing of diflunisal may mitigate disease severity and provide a unique adjunctive tool in the treatment of SA infection.