Biogenic production of nanomaterials gained great importance in nanotechnology industry. Zinc Oxide is one of the most effective antimicrobial agents. Zinc oxide nanoparticles (ZnO-NPs) may be produced cheaply and sustainably for a variety of biomedical uses and water disinfection for removing water pathogens. An efficient reducing and capping agent, Psidium guajava leaves aqueous extract and zinc sulphate (ZnSO4), as precursors were used in this study to biosynthesizeZnO-NPs. Several methods were used to characterize PgZnONPs (Psidium guajava zinc oxide nanoparticles) including X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy(TEM) and UV-Vis Spectroscopy. Disc Diffusion was applied to evaluate Antimicrobial Resistivity of PgZnONPs (Psidium guajava zinc oxide nanoparticles). Thecytotoxicity test preformed against African Green Monkey Kidney cell lines (Vero) using MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide]assay by applying different concentrations. Results indicate resistivity of most tested bacterial and fungal strains with varying degrees. A dose-dependent cytotoxic effect was observed, where 50% cytotoxic concentration (CC50) for ZnSO4 and PgZnONPs (Psidium guajava zinc oxide nanoparticles) were (13.46μg/ml) and (785.20μg/ml) respectively.

Keywords: Antimicrobial Activity - Disc Diffusion - Medicine Industry- Green synthesis of Nanomaterial – Zinc oxide Nonmaterial- guava –Psidium guajava leaves- Water Purification- water disinfection-MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide]assay - Vero Cell Line- Cytotoxicity.

Abbreviation: PgZnONPs: zinc oxide nanoparticles from Psidium guajava leaves extract, PgLE: Psidium guajava leaves extract, XRD: X-Ray Diffraction, SEM: Scanning Electron Microscopy, TEM: Transmission Electron Microscopy, zinc sulphates: ZnSO4, MTT: [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide]assay.