Green Synthesis and Antimicrobial Activities of Silver Nanoparticles using Cell Free-Extracts of Enterococcus species

Abstract

Cell-free extracts of six strains of Enterococcus species obtained from fermented foods were used for the green synthesis of silver nanoparticles (AgNPs), which was characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The biosynthesized AgNPs were dark brown in colour having surface plasmon resonance in the range of 420-442 nm. The spherical shaped AgNPs had sizes of 4-55 nm, whose formations were facilitated by proteins as indicated by the presence of peaks 1,635-1,637 and 3,275-3,313 cm^-1 in the FTIR spectra. The energy dispersive x-ray (EDX) showed prominent presence of silver in the AgNPs colloidal solution, while the selected area electron diffraction was typified by the face-centred crystalline nature of silver. The particles inhibited the growth of multi-drug resistant clinical isolates of Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris, and also potentiated the activities of ampicillin, ciprofloxacin and cefuroxime in the AgNPs-antibiotic synergy studies. In addition, the prospective relevance of the particles as nanopreservative in paints was demonstrated with the inhibition of growth of Staphylococcus aureus, Pseudomonas aeruginosa, Aspergillus niger and A. flavus in AgNPs-paint admixture. This report further demonstrates the green synthesis of AgNPs by strains of Enterococcus species.