Eco-friendly methods for creating nanoparticles have gained attention due to the rising incidence of antibiotic resistance. Zinc oxide nanoparticles (ZnONPs) can be produced sustainably using Cissampelos pareira L., a medicinal plant high in bioactive phytochemicals. In this study, ZnONPs were synthesised using C. pareira extract and their antibacterial efficacy and initial toxicity profile were assessed. During ZnONP synthesis, the aqueous extract of C. pareira performed as a stabilising and reducing agent. The UV-visible spectroscopy confirmed the creation of nanoparticles, revealing a distinctive absorption peak at 350 nm that remained consistent for up to 48 hr. Agar well diffusion and time-kill experiments against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella sp. and Candida albicans were used to determine antimicrobial activity. The brine shrimp lethality test (BSLA) was used to assess preliminary toxicity at dosages between 5 and 80 µg/mL. The ZnONPs showed a species-specific susceptibility pattern and inhibitory effects that were dependent on concentration. The most susceptible species was E. faecalis, with inhibition zones measuring 23.8 ± 1.1 mm and reduced in viable counts of about 2.5 log-1 after 4 hr. While Klebsiella sp. exhibited a minimal susceptibility, moderate inhibitory effects were noted against S. aureus and E. coli. At the highest measured concentration, ZnONPs reduced C. albicans by about 2 log₁¹. Under the tested conditions, BSLA results showed low acute toxicity, with ≥90 % survival at all concentrations. In the BSLA model, C. pareira-mediated ZnONPs showed low acute toxicity and concentration-dependent antimicrobial inhibitory action. Although these results demonstrate the potential of plant-mediated ZnONPs as antimicrobial agents, further characterisation of the nanoparticles, longer stability studies, suitable control experiments and thorough biocompatibility evaluations are needed to confirm their biomedical applicability.
