Silver nanoparticle-protein interactions and the role of lysozyme as an antagonistic antibacterial agent

The photoreductive synthesis and antibacterial activity of silver nanoparticles (AgNP) prepared in the presence of bovine serum albumin (BSA) and lysozyme (LZ) were evaluated. AgNP@BSA showed similar antibacterial activity to those stabilized with citrate (AgNP@CIT) and to an AgNO₃ solution, suggesting the releases of Ag⁺ as the mechanism of death. In contrast, AgNP@LZ solutions showed no activity, although LZ behaves as a moderately antibacterial peptide. Furthermore, the addition of LZ to the AgNP@CIT or AgNP@BSA solutions induced their agglomeration and suppressed their original antibacterial efficacy. This antagonistic antibacterial effect exerted by LZ on AgNPs is associated with electrostatic interactions exerted by LZ. Specific metal-LZ interactions produce a harder protein corona on AgNP@LZ that retains Ag⁺, while LZ acts as a glue for AgNP@CIT or AgNP@LZ due to its opposite electrical charge, besides strong binding to Ag⁺avoiding the bactericide effect. Therefore, bactericidal effects of AgNP in biological media may be modulated by specific protein interactions.