6-gingerol enhances ciprofloxacin efficacy by inhibiting NorA efflux pump in Staphylococcus aureus

The drug efflux mechanism adopted by Staphylococcus aureus helps it in its survival under antibiotic pressure. The efflux pump NorA, a member of the MFS superfamily, effluxes out fluoroquinolones, biocides, quaternary ammonium compounds, and anti-infectives. Therefore, in a continuous effort to identify new scaffolds as NorA inhibitors, we in the present study screened 6-gingerol ((5S)-5-Hydroxy-1-(4-hydroxy-3-methoxyphenyl) decan-3-one) for its role as a NorA efflux pump inhibitor. 6-gingerol dramatically decreased the intracellular invasion and ciprofloxacin minimum inhibitory concentration (MIC) in NorA, overproducing S. aureus SA-1199B. Furthermore, 6-gingerol enhanced the killing efficacy and minimized the mutation frequency of ciprofloxacin. The accumulation of ethidium bromide, another substrate for NorA efflux pump, was significantly inhibited by 6-gingerol. A molecular docking on NorA protein suggested the potential role of 6-gingerol in inhibiting efflux pump via binding at the protein's active site. 6-gingerol showed an excellent binding affinity of −5.8 kcal/mol at NorA protein. Further, in an intracellular invasion assay performed using J774A. 1 macrophage cell lines, 6-gingerol significantly reduced the invasion of S. aureus SA-1199B (NorA overproducing) by 2 Log₁₀. For the first time, the study delineated the role of 6-gingerol as an efflux pump inhibitor of S. aureus with a significant impact on intracellular invasion of the bacteria.