Eco-friendly synthesis of copper nanoparticles by using Ralstonia sp. and their antibacterial, anti-biofilm, and antivirulence activities

Biosynthesized nanoparticles (NPs) created through environmentally friendly and low-toxicity methods show great potential for various nanotechnology applications. In particular, copper nanoparticles (Cu-NPs) are promising for medical uses. This study aims to explore the eco-friendly synthesis of Cu-NPs and their potential as a novel strategy to combat antimicrobial resistance. Cu-NPs were synthesized using <i>Ralstonia</i> sp. KF264453 and characterized with techniques including ultraviolet-visible (UV-Vis) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), zeta potential analysis, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The antibacterial properties of the NPs and their synergistic effects with common antibiotics were assessed. The study also investigated their impact on bacterial cell membrane disruption, biofilm formation, efflux pump activity, and motility. UV-Vis analysis indicated a significant absorption peak at 552 nm, confirming surface plasmon resonance (SPR) for Cu-NPs. FESEM images revealed predominantly spherical NPs with an average size of 69.7 nm. DLS measurements indicated a hydrodynamic diameter of 78.2 nm due to stabilizing biomolecules. A zeta potential of -5.1 mV suggested moderate colloidal stability, suitable for short-term biomedical applications. XRD analysis confirmed a face-centered cubic (FCC) crystalline structure with an average crystallite size of 45 nm. FT-IR spectra detected functional groups, indicating that proteins, carbohydrates, lipids, and amino acids may have contributed to the synthesis and stabilization of the NPs. Cu-NPs showed notable antibacterial efficacy, with minimum inhibitory concentrations (MIC) between 0.625 and 5 μg/mL and minimum bactericidal concentrations (MBC) ranging from 5 to 20 μg/mL. They improved the effectiveness of penicillin and cefixime, enhanced membrane permeability, inhibited biofilm formation, disrupted efflux pump activity in <i>Staphylococcus aureus</i> SA-1199B, and decreased swarming motility in <i>Pseudomonas aeruginosa</i>. Cu-NPs demonstrate strong antimicrobial activity, inhibit biofilm formation and efflux pump function, and enhance the effectiveness of conventional antibiotics. While they show promise in combating antimicrobial resistance, further research is needed to assess their clinical potential and safety for medical use.