Characterization of Silver Nanoparticles Synthesized Using <i>Hypericum perforatum</i> L. and Their Effects on <i>Staphylococcus aureus</i>

This study investigates the synthesis of silver nanoparticles (AgNPs) using Hypericum perforatum L. and evaluates their antibacterial and antibiofilm activities against Staphylococcus aureus. The synthesized AgNPs were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). UV-Vis spectroscopy showed a maximum absorption peak at 448 nm, which indicates that nanoparticles have been formed successfully. TEM analysis showed that the AgNPs were spherical, with an average size of 35 ± 2.7 nm. FTIR confirmed the presence of functional groups on the surface of AgNP that may be contributing to its biological activity. The AgNPs exhibited significant antibacterial activity, with a minimum inhibitory concentration (MIC) of 75 μg/mL and an inhibition zone of 13 ± 0.13 mm at this concentration. They were also highly effective in inhibiting biofilm formation even at a concentration of 25 μg/mL, reducing biofilm formation by 47.25% ± 3.51%. At increased concentrations, nanoparticles have been shown to compromise bacterial membranes, leading to significant membrane disruption. This disruption subsequently results in a reduction of cellular respiration, with observed decreases of approximately twofold when compared to controls. Additionally, nanoparticles facilitate the production of superoxide anions, which can rise by about threefold, consequently enhancing the overall effectiveness of bacterial inactivation. Field emission scanning electron microscopy (FE-SEM) revealed structural damage to bacterial cells treated with AgNPs, supporting their antimicrobial effects. These findings suggest that AgNPs synthesized from H. perforatum could serve as effective antimicrobial agents against S. aureus. Their ability to disrupt bacterial cell membranes, inhibit respiration, and induce oxidative stress makes them promising candidates for antimicrobial and antibiofilm applications, particularly given the increasing concern over bacterial resistance to conventional antibiotics.