Biogenic Synthesis of Antibacterial and Antioxidant Silver Nanoparticles Using Enterococcus faecium DU.FS-Derived Exopolysaccharides: A Sustainable Approach for Green Nanotechnology

Green synthesis of nanoparticles is an effective, cost-effective, and environmentally friendly approach to produce biocompatible nanoparticles with broad-spectrum bioactivities. In the current study, lactic acid bacterium-derived exopolysaccharide (EPS) was explored to biologically synthesize green silver nanoparticles (EPS-AgNPs). The antibacterial and antioxidant activities of EPS-AgNPs were investigated by agar well diffusion and DPPH tests, respectively. Subsequently, EPS-AgNPs and chemical AgNPs were characterized, and their physicochemical properties were compared. According to 16 S rRNA gene sequencing, the EPS-producing lactic acid bacterium showed 97.77% similarity to Enterococcus faecium. EPS-AgNPs exhibited inhibitory effects on Gram-positive and Gram-negative bacterial pathogens. Additionally, EPS-AgNPs showed considerable ability (84%) to quench DPPH free radicals. Fourier-transform infrared spectroscopy (FT-IR) showed the involvement of EPS’s functional groups, including hydroxyl, carbonyl, and aldehyde groups, in synthesizing nanoparticles. Scanning electron microscopy revealed a quasi-spherical morphology for both the EPS-AgNPs and chemically synthesized AgNPs, while X-ray diffraction (XRD) analysis confirmed their crystalline nature. The high metal content of chemical Ag-NPs (89.79%) was in good agreement with its high thermal stability in TGA results. Additionally, lower thermal stability and less Ag content (65.93%) of EPS-AgNPs, along with their smooth surfaces, indicated the capping role of EPS. EPS-AgNPs showed Z-average size, PI value, and zeta potential of 158.31 nm, 0.29, and − 17.75 mV, respectively. Collectively, the present study revealed that Enterococcus faecium-derived EPS acted as reducing, capping, and stabilizing agents in green synthesizing EPS-AgNPs with potential applications in medical and food-packaging industries.