Mocravimod as a repurposing drug against clinical isolates of Staphylococcus aureus by targeting cell membrane

Staphylococcus aureus infections, particularly those caused by multidrug-resistant strains and associated with biofilm formation, pose a major therapeutic challenge in clinical practice. The objective of this study was to evaluate the antibacterial and antibiofilm activity of mocravimod (KRP-203), an FDA-approved S1P receptor modulator, against clinical S. aureus isolates and to explore its underlying mechanism of action. The antibacterial activity of KRP-203 was assessed against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) using MIC determination, time-kill assays, and biofilm inhibition models. KRP-203 exhibited strong bactericidal activity against planktonic MSSA and MRSA, with MIC values ranging 6.25–50μM. Time-kill assays demonstrated rapid bacterial eradication at 8× MIC within 2 h, showing superior killing kinetics compared with vancomycin. At sub-inhibitory concentrations, KRP-203 inhibited biofilm formation by up to 70% and reduced viable bacterial counts in mature biofilms by >2.5 logs. To elucidate the antibacterial mechanism, whole-genome sequencing and quantitative proteomic analyses were performed. These analyses revealed mutations in membrane-associated genes, including glnQ and BCAT, and significant alterations in proteins related to membrane integrity and redox regulation. Consistently, functional assays confirmed that KRP-203 disrupts bacterial cell membrane, as evidenced by dose-dependent membrane depolarization, increased permeability, and direct binding to cardiolipin and phosphatidylglycerol. Molecular docking further predicted a favorable interaction between KRP-203 and GlnQ. In conclusion, KRP-203 demonstrated notable antibacterial and antibiofilm activity against S. aureus, likely through membrane integrity disruption. While these findings highlight its potential as a repurposed antibacterial agent, further studies are required to fully elucidate its molecular targets, optimize antibacterial efficacy, and evaluate its in vivo safety profile.