Bioflavonoid Baicalein Modulates Tetracycline Resistance by Inhibiting Efflux Pump in <i>Staphylococcus aureus</i>

The rise in antibiotic resistance among bacterial pathogens, particularly <i>Staphylococcus aureus</i>, has become a critical global health issue, necessitating the search for novel antimicrobial agents. <i>S. aureus</i> uses various mechanisms to resist antibiotics, including the activation of efflux pumps, biofilm formation, and enzymatic modification of drugs. This study explores the potential of baicalein, a bioflavonoid from <i>Scutellaria baicalensis</i>, in modulating tetracycline resistance in <i>S. aureus</i> by inhibiting efflux pumps. The synergistic action of baicalein and tetracycline was evaluated through various assays. The minimum inhibitory concentration (MIC) of baicalein and tetracycline against <i>S. aureus</i> was 256 and 1.0 μg/mL, respectively. Baicalein at 64 μg/mL reduced the MIC of tetracycline by eightfold, indicating a synergistic effect (fractional inhibitory concentration index: 0.375). Time-kill kinetics demonstrated a 1.0 log CFU/mL reduction in bacterial count after 24 hours with the combination treatment. The ethidium bromide accumulation assay showed that baicalein mediated significant inhibition of efflux pumps, with a dose-dependent increase in fluorescence. In addition, baicalein inhibited DNA synthesis by 73% alone and 92% in combination with tetracycline. It also markedly reduced biofilm formation and the invasiveness of <i>S. aureus</i> into HeLa cells by 52% at 64 μg/mL. These findings suggest that baicalein enhances tetracycline efficacy and could be a promising adjunct therapy to combat multidrug-resistant <i>S. aureus</i> infections.