Silybin-conjugated gold nanoparticles for antimicrobial chemotherapy against Gram-negative bacteria

Abstract

Gold nanoparticles (AuNPs) have emerged as an interesting tool with high potential in the medical field and as a promising alternative against multidrug-resistant microorganisms. Green chemical synthesis of AuNPs conjugated with the flavonoid silybin (S) to generate a nano-system with dual antibacterial and antioxidant properties were performed. The S-AuNPs plasmon peak was found at 567 nm with narrow particle size distribution of around 58 nm. TEM and AFM images revealed the presence of spherical and homogeneous nanoparticles with an average diameter of 35 nm. Conjugation of silybin to the surface of AuNPs was confirmed by FTIR analysis. Antioxidant properties were found since the S-AuNPs were able to prevent the rapid oxidation of Brilliant Cresyl Blue, as reporter dye, in presence of sodium hypochlorite as strong oxidant. Also, S-AuNPs inactivated Gram-negative bacteria of nosocomial interest such as Pseudomonas aeruginosa and Escherichia coli. A minimum inhibitory concentration of 11.2 and 5.6 μg/ml was observed for each microbe respectively. Fluorescent live/dead assay confirmed that S-AuNPs can kill bacteria with significant cell damage only after 30 min of exposition. TEM images showed that S-AuNPs can strongly interact with bacteria surfaces leading to cell lysis. Also, S-AuNPs showed about half of cytotoxic concentration (CC50) compared within acyclovir (control) tested in Vero cells.