Oxadiazolone Derivatives: Powerful Tools to Reduce Staphylococcus aureus Infection.

Staphylococcus aureus is a Gram-positive opportunistic pathogen and a top priority bacterium in the fight against antimicrobial resistance. Its high propensity to develop resistance, its high virulence, and its ability to form biofilms and persist intracellularly result in difficult-to-treat infections against, which new chemical classes are urgently needed. Here, we investigated the antibacterial activity of oxadiazolone-core derivatives (OX) against planktonic, intracellular, and biofilm-associated S. aureus. Among the tested compounds, MpPPOX exhibited a bactericidal effect on extracellular bacteria with an MIC similar to that of vancomycin; iBPOX mainly inhibited intracellular replication, while HPOX strongly impaired initial biofilm formation. These results prompted us to identify the potential target enzymes of the three OXs via activity-based protein profiling, combined with mass spectrometry. The antibiofilm HPOX compound was indeed found to primarily react with enzymes involved in biofilm formation and associated virulence, while iBPOX and the most active MpPPOX inhibitor targeted multiple (Ser/Cys)-based enzymes. Among these, the FabH protein has been confirmed as a vulnerable target of MpPPOX. Overall, this study underscores the multitarget nature of the OXs, which covalently bind to several (Ser/Cys)-based enzymes of interest. Such property makes them highly versatile chemotypes that could be used as broad-spectrum antimicrobial agents, notably by improving the antibiofilm activity of ineffective or poorly active drugs.