Zanthoxylum beecheyanum enhances vancomycin activity and inhibits biofilm formation in resistant staphylococcus...

The increasing prevalence of multidrug-resistant Staphylococcus aureus continues to compromise the effectiveness of conventional antimicrobial therapy and highlights the need for novel adjunctive treatment strategies. Despite the traditional medicinal use of Zanthoxylum species, the antibacterial potential of Zanthoxylum beecheyanum remains largely unexplored. Here, we characterized the chemical composition of Zanthoxylum beecheyanum essential oil (ZBEO) and evaluated its antibacterial activity against a panel of clinically relevant S. aureus strains, its ability to potentiate vancomycin activity, and its effects on biofilm formation. GC-MS profiling identified D-limonene and methyl cinnamate as the predominant volatile metabolites. ZBEO exhibited antibacterial activity against all tested strains, with MIC values ranging from 8 to 128 mg/L. Checkerboard assays demonstrated synergistic effects between ZBEO and vancomycin, with fractional inhibitory concentration index values as low as 0.375. Time-kill assays showed that ZBEO exhibited antibacterial activity as monotherapy and, in combination, enhanced bacterial killing and reduced bacterial regrowth compared with vancomycin alone. In addition, ZBEO inhibited biofilm formation in a concentration-dependent manner, with the greatest activity observed during combination treatment with vancomycin. Preliminary safety assessment demonstrated low hemolytic activity and limited cytotoxicity toward HEK-293 cells (CC₅₀ > 128 mg/L) within the antibacterial concentration range. These findings identify ZBEO as a promising adjunct to vancomycin for enhancing antibacterial activity and inhibiting S. aureus biofilm formation, warranting further investigation as a plant derived adjunctive therapy for difficult-to-treat staphylococcal infections.