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

Biofilms are multicellular communities of microbial cells that grow on natural and synthetic surfaces. They have become the major cause for hospital-acquired infections because once they form, they are very difficult to eradicate. Nanotechnology offers a new approach to fight biofilm-associated infections. Here, we report on the synthesis of silver nanoparticles (AgNPs) with antibacterial ligand epigallocatechin gallate (EGCG) and the formation of lysozyme protein corona on AgNPs as shown by UV-Vis, dynamic light scattering, and circular dichroism analyses. We further tested the activity of EGCG-AgNPs and their lysozyme bioconjugates on the viability of Bacillus subtilis cells and biofilm formation. Our results showed that, although EGCG-AgNPs presented no antibacterial activity on planktonic Bacillus subtilis cells, they inhibited B. subtilis biofilm formation at concentrations larger than 40 nM and EGCG-AgNP-lysozyme bioconjugates inhibited biofilms at concentrations above 80 nM. Cytotoxicity assays performed with human cells showed a reverse trend, where EGCG-AgNPs barely affected human cell viability, while EGCG-AgNP-lysozyme bioconjugates severely hampered viability. Our results therefore demonstrate that EGCG-AgNPs may be used as non-cytotoxic antibiofilm agents.