Green fabrication and antibacterial evaluation of lysozyme-immobilized cysteine-capped silver nanoparticles

The broad-spectrum antibacterial properties of silver nanoparticles (AgNPs) are attracting increasing attention as a means to combat drug-resistant infections. Herein, we describe the green production of AgNPs with minimal environmental impact by using plant components as reducing agents.

Hibiscus rosa sinensis flower extract was used to form AgNPs from a 1 mM solution of silver nitrate. The NPs were cysteine-stabilized, on which hen egg white lysozyme was immobilized. The NPs, as analyzed by SEM, were nearly spherical. The size of the Cys-NPs, as measured by TEM, ranged from 12.52 nm to 27.20 nm, with an average size of 22.83, and the size of Lys-Cys-AgNPs ranged from 16.32 nm to 44.60 nm, with an average size of 30.30 nm. The enzyme assay for Lys-Cys-AgNPs demonstrated an effective activity of approximately 80.8 ± 3.6% compared to free lysozyme, and the immobilization efficiency was calculated to be 66.8%. MIC of Lys-Cys-AgNPs against E. coli (8.5 μg/mL), P. aeruginosa (12 μg/mL), S.aureus (6 μg/mL) and S. mutans (5.5 μg/mL). The antibacterial activity of Lys-Cys-AgNPs combined with streptomycin was evaluated against E. coli, P. aeruginosa, S. aureus, and S. mutans using the agar well diffusion method. The zones of inhibition observed were 11.00 ± 0.31 mm, 8.00 ± 0.11 mm, 8.00 ± 0.14 mm and 18.00 ± 0.65 mm, respectively.

Green-synthesized, cysteine-stabilized silver nanoparticles functionalized with lysozyme demonstrated enhanced antibacterial efficacy against both Gram-positive and Gram-negative pathogens. These findings highlight their potential as an eco-friendly and effective nanobiotherapeutic strategy to combat drug-resistant infections.