Inhibitory effect of EGCG-AgNPs and their lysozyme bioconjugates on biofilm formation and cytotoxicity

Abstract

Multidrug resistance of pathogenic bacteria to antimicrobial drugs has become a major problem for the diagnosis and treatment of infectious diseases. Here, we report on the synthesis of silver nanoparticles (AgNPs) with epigallocatechin gallate (EGCG) ligand, which is known to present antibacterial activity. We further describe the interaction of EGCG-AgNPs with lysozyme, an antibacterial enzyme abundant in fluids like serum, saliva and tears, and the formation of EGCG-AgNP-lysozyme bioconjugates. Our results demonstrate the formation of lysozyme protein corona as shown by UV-Vis, dynamic light scattering and SDS-PAGE analyses. Using circular dichroism spectroscopy we found that lysozyme preserves its secondary structure at low concentration of EGCG-AgNPs, whereas higher concentrations induce protein structural changes. Furthermore, we have shown in bacterial growth and biofilm formation assays that EGCG presents no antibacterial activity on planktonic Bacillus subtilis cells when it was bound to AgNPs. It was found that EGCG-AgNPs (>40 nM) inhibit B. subtilis in biofilm forming conditions and the inhibition effect is reduced by lysozyme corona formation on EGCG-AgNPs. Our results demonstrate that EGCG-AgNPs could be used as antibiofilm agents because they showed lower cytotoxicity and significant inhibitory effect on pellicle formation.