Green-synthesised silver nanoparticles using sewage-derived fish gut bacteria with antibacterial potential against AmpC-β producing Escherichia coli

Microbial-mediated green synthesis of silver nanoparticles (AgNPs) represents an eco-friendly alternative to conventional chemical methods by utilising biological reducing and stabilising agents. In this study, gut bacteria isolated from sewage-exposed fish were used to synthesise AgNPs, and the resulting nanoparticles were evaluated for their antimicrobial and antioxidant activities. Bacterial biomass was used to reduce Ag + ions from a 1 mM AgNO 3 solution. Nanoparticle formation and characterisation were confirmed using UV–Visible spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD). A distinct color change from pale yellow to brown and a characteristic absorption peak at approximately 350–400 nm confirmed AgNP synthesis. TEM analysis revealed predominantly spherical nanoparticles ranging from 10 to 30 nm in size. The biosynthesised AgNPs exhibited antibacterial activity against both Gram-positive and Gram-negative bacteria including AmpC-producing Escherichia coli , producing inhibition zones in the range of 24–31 mm. The synthesised nanoparticles displayed strong dose-dependent antioxidant activity, in terms of DPPH and ABTS + radical scavenging activity, with IC 50 of 18 μg/mL and 39 μg/mL, respectively. These findings indicate the potential of sewage fish gut bacteria as a sustainable source for producing bioactive AgNPs with promising applications as an antibacterial agent.