Preparation of silibinin- dendrimer-stabilized Au nanoparticles for decreasing vancomycin resistance in S. aureus clinical isolates.

INTRODUCTION

Silibinin (SB), a bioactive flavonolignan derived from milk thistle seeds (Silybum marianum L.), exhibits well-documented antioxidant, antibacterial, antifungal, antiviral, and hepatoprotective activities. This study aimed to conjugate SB with fourth-generation poly(amidoamine) dendrimer-stabilized gold nanoparticles (DSA) to enhance its solubility and evaluate its antibacterial efficacy against clinical isolates of Staphylococcus aureus (S. aureus).

METHODS

The morphology and structural features of silibinin-dendrimer-stabilized gold nanoparticle complex (SB-DSA) were characterized using Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FE-SEM). Antibacterial activity was assessed through biofilm formation assays, checkerboard analysis, and quantitative real-time PCR (qRT-PCR) using clinical S. aureus isolates and a standard reference strain.

RESULTS

Physicochemical analyses confirmed the successful incorporation of SB into the DSA matrix. The average particle size of the SB-DSA nanocomposites was approximately 20 nm. A synergistic interaction between SB-DSA and vancomycin was observed, with SB-DSA significantly enhancing the susceptibility of vancomycin-resistant isolates to vancomycin. Biofilm formation was markedly reduced in resistant isolates treated with the SB-DSA/vancomycin combination compared with vancomycin alone. The time-kill kinetics of SB-DSA in the tested isolates ranged from 4 to 8 h. Combination treatment also resulted in downregulation of icaA, and norA expression in resistant S. aureus isolates.

CONCLUSION

Silibinin encapsulated within DSA demonstrates potent anti S. aureus activity, likely mediated through downregulation of efflux pump-related genes and improved intracellular retention of vancomycin. Consequently, even low concentrations of vancomycin, when combined with silibinin, effectively inhibited the growth of vancomycin-resistant isolates.