2-Aminothiophene derivatives reduce resistance to fluoroquinolones in Staphylococcus aureus strains which overexpress NorA and MepA efflux pumps

Abstract

In response to the growing threat of antibiotic resistance, this study aimed to identify novel compounds capable of modulating and/or even restoring antibiotic efficacy by inhibiting bacterial efflux pumps. Thirteen 2-aminothiophene (2-AT) derivatives were synthesized and tested against Staphylococcus aureus strains overexpressing NorA and MepA pumps, which confer resistance to fluoroquinolones. Although the 2-ATs displayed little inherent antibacterial activity, several—particularly compounds P4, P7, and P8—significantly potentiated the effects of norfloxacin, ciprofloxacin, and ethidium bromide (EtBr), reducing their Minimum Inhibitory Concentrations (MICs) by up to fourfold. P7 and P8, both 2-aminoselenophene bioisosteres, emerged as especially effective, demonstrating strong efflux pump inhibitory (EPI) activity and, for the first time, confirming their ability to inhibit MepA-mediated efflux in S. aureus. Cytotoxicity assays on VeroE6 and HepG2 cell lines confirmed the safety profile of selected compounds. EtBr accumulation assays and molecular dynamics simulations further supported the mechanism of action, confirming that these derivatives inhibit efflux activity. Overall, the results highlight the potential of 2-AT derivatives—especially P7 and P8—as promising EPIs to combat fluoroquinolone-resistant S. aureus.