Extracellular biosynthesis of silver nanoparticles using aquatic bacterial isolate and its antibacterial and antioxidant potentials

Abstract

The use of microorganisms in the synthesis of nanoparticles emerges as an eco-friendly and exciting approach. Silver bionanoparticles (AgNPs) are known to own inhibitory and bactericidal effects. This study focuses on the biosynthesis of silver nanoparticles (AgNPs) using the culture filtrate of Enterococcus faecalis S7, isolated from Al-Bahr El-Pherony, Menoufyia Governorate, Egypt, and evaluation of its antibacterial and antioxidant potency. AgNO3 solution (1 mM) was added to the cell-free culture supernatant, and also the mixture was incubated at 37 °C for 24 h in an orbital shaker (120 rpm). The AgNPs were characterized using UV–visible spectroscopy, X-ray Diffraction (XRD), EDAX, FTIR, and Transmission Electron Microscopy (TEM). Bio-manufactured silver nanoparticles were tested for their antibacterial and antioxidant activity using agar well diffusion and DPPH assays, respectively. The nanoparticles exhibited maximum absorbance at 430 nm in UV–Vis spectroscopy. The XRD spectrum exhibited 2Ɵvalues corresponding to the silver nanocrystals. TEM micrographs revealed the extracellular formation of spherical nanoparticles within the size range of 10–16 nm. The as-formed AgNPs exhibited antibacterial activity against the tested bacterial species Escherichia coli, Salmonella sp.; Vibrio cholerae, Pseudomonas aeruginosa and Staphylococcus aureus with a maximum inhibition zone of 30 mm against S. aureus. Furthermore, bacterial mediated AgNPs showed antioxidant activity in a dose-dependent manner. The data evaluated by this study provided evidence of AgNPs being a potent antioxidant and antibacterial compounds against both Gram-positive and Gram-negative bacteria. These results suggested that AgNPs can be used as an adjuvant for the treatment of infectious diseases.