Evaluation of in vitro antibacterial efficacy of biogenic Ag-ZnO nanocomposites synthesized utilizing Suprema F1 agro-waste

Abstract

This study investigated the antimicrobial properties of Ag-ZnO nanocomposites (NCs) synthesized from agro-waste derived from the Suprema F1 pumpkin variety, including peels, seeds, and leaves. The current study aimed to evaluate the antibacterial activity of pumpkin agro-waste-mediated Ag-ZnO NCs, targeting drug-resistant pathogens. Aqueous agro-waste-mediated Ag-ZnO NCs were synthesized under various optimization conditions and characterized under UV-vis spectroscopy, FTIR, SEM, TEM, and XRD analysis. The antibacterial effectiveness of biogenic AgNPs, ZnO NPs, and Ag-ZnO NCs with various concentrations (500 ppm, 1000 pm, 2000 ppm) was evaluated and compared against Escherichia coli and Staphylococcus aureus. The positive controls used for comparison were Azithromycin and Tetracycline, respectively (2000 ppm: 100 μL). The formation of Ag-ZnO NCs was identified through surface plasmon resonance peaks ranging from 350–450 nm. SEM analysis confirmed the successful synthesis of Ag-ZnO NCs by showing spherical AgNPs aggregating on the ZnO surface. TEM analysis unveiled that the particle size distribution of the NMs ranged between 20 and 210 nm. XRD analysis indicated a hexagonal wurtzite structure observed for pure ZnO NPs and a face-centered structure for AgNPs. The antibacterial activity of NMs exhibited an increasing trend with AgNPs > Ag-ZnO NCs > ZnO NPs. The largest inhibition zones observed for seed-mediated AgNPs (2000 ppm: 100 μL) against E. coli and S. aureus were 20 mm, while for Ag-ZnO NCs, the values were 17 mm and 19 mm, respectively. Regarding the inhibitory effects of ZnO NPs, it was observed that leaf-mediated ZnO NPs (2000 ppm: 100 μL) displayed the greatest inhibition zones, with 14 mm against both bacterial strains. The ability of growth inhibition against S. aureus was insignificant (p≥0.05) between seed and leaf-mediated AgNPs and Ag-ZnO NCs. There were insignificant differences (p≤0.05) between leaf-mediated AgNPs and Ag-ZnO NCs. Azithromycin and Tetracycline (2000 ppm: 100 μL) exhibited growth inhibition of 35 mm against E. coli and 50 mm against S. aureus, respectively. These findings emphasize that NMs derived from pumpkin agro-waste demonstrated substantial antibacterial effects.