Biogenic Silver Nanoparticles as Dual-Action Antibacterial and Antibiofilm Agents Against Opportunistic Pathogens

Abstract

The increasing resistance of pathogenic bacteria and their tendency to form biofilms on medical instruments highlight the urgent need for novel antimicrobial approaches. This study focused on the eco-friendly synthesis of silver nanoparticles (AgNPs) using Mentha longifolia leaf extract and evaluated their antibacterial and antibiofilm efficacy against selected opportunistic pathogens. Aqueous extracts prepared from fresh M. longifolia leaves served as both reducing and capping agents in the green synthesis of AgNPs from silver nitrate. The successful formation of nanoparticles was indicated by a visible color shift and confirmed through UV-Vis spectroscopy, FTIR, SEM, and XRD techniques. The AgNPs produced were predominantly spherical, slightly agglomerated, and crystalline, with an estimated mean diameter of 43 nm. Their antibacterial potential was tested using the agar well diffusion method against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. Notable antimicrobial activity was observed, especially at a concentration of 50 μg/mL. The antibiofilm effect was quantified via a microtiter plate assay, showing that the ML-mediated AgNPs substantially suppressed biofilm formation across all tested bacterial strains, with inhibition rates reaching up to 76%. Statistical analysis confirmed that these effects were significant (p < 0.05). Overall, the study demonstrates that AgNPs synthesized via M. longifolia extract possess potent antibacterial and antibiofilm properties, offering a sustainable and effective alternative for combating infections linked to resistant and biofilm-producing bacteria