Green-Synthesized Copper Nanoparticles Derived from Fermented Foxtail Millet Polyphenols Exhibit Antibacterial and Antibiofilm Activity Against Ralstonia solanacearum

Abstract

Introduction: Ralstonia solanacearum is a destructive soil-borne bacterium responsible for bacterial wilt in several economically important crops, including tomato, potato, banana, and eggplant. The persistence of this pathogen and increasing concern regarding antimicrobial resistance have encouraged the development of environmentally friendly disease management strategies. Materials and Methods: In the present study, copper nanoparticles (CuNPs) were synthesized through a green synthesis approach using polyphenols extracted from fermented foxtail millets. The synthesized nanoparticles were characterized using UVvisible spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and scanning electron microscopy (SEM). Antibacterial activity of the synthesized nanoparticles against R. solanacearum was evaluated using agar well diffusion, minimum inhibitory concentration (MIC), and biofilm inhibition assays with standard protocols. Results: In the broth dilution assay, optical density decreased from 1.56 0.12 to 0.16 0.09 at 400 µgmL. The nanoparticles also exhibited strong antibiofilm activity, showing approximately 84 inhibition after 15 h of incubation, whereas the polyphenol extract alone exhibited 41 inhibition. Conclusion: These findings indicate that polyphenol-mediated copper nanoparticles possess promising antibacterial properties and may represent a sustainable approach for managing plant pathogens such as R. solanacearum.