Investigation of antimicrobial effects of ZnO nanoparticles synthesized by various methods on S. aureus

In this study, zinc oxide nanoparticles (ZnO-NPs) were synthesized using both environmentally friendly biosynthesis and chemical synthesis methods. For chemical synthesis, the sol-gel method was employed, using zinc acetate dihydrate (Zn(C₂H₃O₂)₂·2H₂O) as the precursor. In the biosynthesis method, ZnO-NPs were produced using dried and calcined forms of cells and supernatant from the Rhodopseudomonas palustris strain. During the biological synthesis process, different zinc salts—zinc acetate dihydrate (Zn(C₂H₃O₂)₂·2H₂O), zinc sulfate heptahydrate (ZnSO₄·7H₂O), and zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O)—were employed to evaluate their effects on synthesis efficiency, particle morphology, and the structural properties of the ZnO-NPs. The physical and chemical properties of the synthesized nanoparticles were characterized using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FT-IR), and UV-Vis Spectrophotometry. Additionally, the antibacterial and antibiofilm activities of these nanoparticles against Staphylococcus aureus ATCC 25923 were investigated. The antibacterial and antibiofilm effects of the synthesized nanoparticles on S. aureus were evaluated. In the agar diffusion test used to determine antibacterial activity, the highest efficacy was observed in the KS group, with an inhibition zone of 2.5 cm. In contrast, inhibition zone diameters in the KSA, KSN, and KSS groups were determined to be 1.2 cm. In the other nanoparticle groups, zone diameters remained below 1 cm. No antibacterial activity was observed in the YHA, YSA, and YHS groups. Additionally, as a result of the analyses conducted on biofilm formation, it was determined that the YHA, YSA, and YHS groups led to biofilm formation at levels similar to the positive control. These findings support that these groups do not exhibit antibiofilm activity. The minimum inhibitory concentration (MIC) values effective against S. aureus were mostly determined to be 150, 100, and 75 µg/mL, and these findings were confirmed by minimum bactericidal concentration (MBC) tests. The study also analyzed the effects of effective ZnO-NPs on the expression levels of S. aureus biofilm-associated genes (icaA, icaB, icaC, icaD, fnbA, fnbB, clfA, clfB, fib, ebps, eno, cna, agrA, agrB) using RT-qPCR. Accordingly, in the presence of KS, KSA, KSN, and KSS nanoparticles, significant changes were identified in the expression levels of the ica, fib, ebps, clfB, and fnbB genes. Specifically, in the presence of KS nanoparticles, the expression levels of icaB, icaC, and ebps; in the presence of KSA nanoparticles, icaB and clfB; in the presence of KSN nanoparticles, icaB and icaC; and in the presence of KSS nanoparticles, clfB and fnbB genes were significantly reduced KEYWORDS: Nanotechnology, biotechnology, nanoparticle, Staphylococcus aureus, biofilm