Antibacterial Efficacy and Cytotoxic Assessment of Zinc Oxide Nanoparticles Synthesized Using Bacillus licheniformis

The biosynthesis of zinc oxide nanoparticles (ZnO NPs) was successfully conducted using Bacillus licheniformis ATCC 4527, demonstrating its potential as a safe and efficient bio-nanofactory. The formation of ZnO NPs was confirmed and characterized through multiple analytical techniques, including transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), ultraviolet-visible (UV–Vis) spectroscopy, and zeta potential analysis. The UV–Vis spectrum exhibited a characteristic absorption peak at 349 nm, while the XRD results confirmed the crystalline nature of the nanoparticles. The zeta potential value of –22.9 mV indicated strong negative surface charges, contributing to the colloidal stability of the ZnO NPs. FTIR analysis further verified the presence of biomolecules, particularly proteins, involved in nanoparticle stabilization. The synthesized ZnO NPs exhibited particle sizes ranging from 21 to 35 nm. The antibacterial potential of the ZnO NPs was evaluated against selected Gram-positive and Gram-negative bacterial strains, including Bacillus cereus ATCC 6633, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Klebsiella pneumoniae ATCC 33495. Results revealed significant, dose-dependent antibacterial activity. Additionally, cytotoxicity assessment against the Vero cell line demonstrated a CC₅₀ value of 145.12 ± 1.88 μg/mL, suggesting acceptable biocompatibility at lower concentrations. These findings highlight the potential of biosynthesized ZnO NPs as promising antimicrobial agents for pharmaceutical, medical, and industrial applications, particularly in combating multidrug-resistant bacterial pathogens.