Inhibition of efflux pumps by FDA-approved drugs oxiconazole and sertaconazole restores antibiotic susceptibility in multidrug-resistant <i>S. aureus</i>

Antibiotic resistance in <i>Staphylococcus aureus</i> causes major concern worldwide. In <i>S. aureus</i>, efflux pumps are mostly responsible for the development of multidrug resistance. Active removal of antibiotics from cells by <i>S. aureus</i> efflux pumps, including NorA, NorB, AbcA, and MepA, helps to lower their intracellular concentration and effectiveness. The present study examined two FDA-approved antifungal medications, oxiconazole and sertaconazole, as possible efflux pump inhibitors (EPIs) against multidrug-resistant <i>S. aureus</i>. Our results showed that both drugs reduced the efflux pump activity of drug-susceptible (ATCC25923) and multidrug-resistant (Mu50) <i>S. aureus</i> strains. While sertaconazole inhibited the efflux pumps without changing the efflux rate, oxiconazole lowered both efflux pump activity and efflux rate. Neither of these drugs impacted bacterial membrane integrity nor bacterial growth. Both drugs enhanced the efficacy of norfloxacin, cefotaxime, and moxifloxacin by lowering the MIC values and showed minimal cytotoxicity toward mammalian cells. In combination with the antibiotics, both sertaconazole and oxiconazole significantly lowered the bacterial load in a murine skin infection model. Our results suggested that the drugs altered the proton motive force (PMF), which resulted in diminished membrane potential (Δ<i>Ψ</i>) and an increased electrochemical gradient (ΔpH), thereby inhibiting ATP production and efflux pump activity. The safety profile and potential to enhance antibiotic efficacy suggest that sertaconazole and oxiconazole may be used as EPIs for combating multidrug-resistant <i>S. aureus</i> infections. Further studies are required to assess their pharmacokinetics, toxicity, and activity against a wide range of <i>S. aureus</i> isolates.