Hybrid silver–gold nanoparticles suppress drug resistant polymicrobial biofilm formation and intracellular infection

Abstract

Over decades bacteria have evolved multiple mechanisms to fight antibiotics. Biofilm formation by bacteria is one such mechanism as it forms a barrier and creates an acidic environment that reduces the efficiency of antimicrobials. Bacteria have also developed the ability to persist intracellularly within mammalian cells, causing recurrent infections. Many antibiotics are rendered ineffective due to poor penetration across biofilms and within mammalian cells. In this study, silver–gold hybrid nanoparticles were developed as anti-microbial agents to combat biofilm formation and intracellular infections. Biogenic hybrid silver gold nanoparticles were developed in an organic solvent free single reaction mixture using quercetin, a flavonoid, as the reducing and stabilizing agent. Silver–gold nanoparticles of 40 ± 10 nm diameter were effective against a broad spectrum of bacteria with minimum bactericidal concentrations of 10 μg ml⁻¹ and 20 μg ml⁻¹ for Gram negative and Gram-positive organisms, respectively. These nanoparticles were also effective against mixed infections at 20 μg ml⁻¹. Their mode of action involves generating intracellular oxidative stress in both Gram negative and Gram-positive bacteria, which causes damage to the cell wall. Polymicrobial biofilm formation was suppressed and intracellular infection was reduced by 70% to 90% in fibroblast and monocyte cell lines. These results indicate that hybrid silver gold nanoparticles are promising agents to suppress biofilm formation and tackle intracellular infections.