Strong Antimicrobial Activity of Silver Nanoparticles Obtained by the Green Synthesis in Viridibacillus sp. Extracts.

Priyanka Singh,Ivan Mijakovic

doi:10.3389/fmicb.2022.820048

Abstract

Recently, green silver nanoparticles (G-AgNPs) have gained much attention in medical science due to their extraordinary effects against multidrug-resistant microorganisms. The strong antimicrobial nature of G-AgNPs corresponds to their unique physicochemical properties such as size, shape, surface charge, and active surface groups available to interact with the pathogens. The current study demonstrates a simple, environmentally friendly, and economical method to produce G-AgNPs from an environmental isolate of Viridibacillus sp. The produced G-AgNPs were characterized by various analytical methods, including UV-Vis spectroscopy, single-particle inductively coupled plasma-mass spectrometry (sp-ICP-MS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). The reduction of Ag+ to Ag° was observed by UV-Vis spectroscopy, which demonstrated the formation of stable G-AgNPs with a Surface Plasmon Resonance (SPR) band at the maximum of 430 nm. TEM analysis demonstrated that the G-AgNPs were spherical with a 5–30 nm size range. The produced G-AgNPs were stable for more than 1 year in an aqueous solution at 4°C. Importantly, G-AgNPs showed remarkable antimicrobial activity against Gram-negative pathogens- E. coli and P. aeruginosa with MIC values of 0.1 and 4 μg/mL and MBC values of 1 and 8 μg/mL, respectively. This level of antimicrobial activity is superior to other AgNPs reported in the literature.

Highlights

Silver nanoparticles (AgNPs) are widely known for their industrial applications in the field of medicine, pharmacology, food, agriculture, cosmetics, and textiles due to their unique antimicrobial properties, which further depend on nanoparticles (NPs) structure (Gherasim et al, 2020)
The supernatant showed a visible color change from pale yellow to deep brown, which is attributed to the surface plasmon resonance (SPR) property of G-AgNPs (Ronavari et al, 2021)
The cell-free supernatant of environmental isolate Viridibacillus sp. acted as a reducing and stabilizing agent, which led to the formation of highly stable and monodisperse G-AgNPs

Summary

Introduction

Silver nanoparticles (AgNPs) are widely known for their industrial applications in the field of medicine, pharmacology, food, agriculture, cosmetics, and textiles due to their unique antimicrobial properties, which further depend on nanoparticles (NPs) structure (Gherasim et al, 2020). These limitations motivate the development of green alternative methodologies, which leads to the formation of uniform and stable NPs with a biocompatible layer (called the corona) around them (Singh et al, 2016a; Heinemann et al, 2021) These green nanoparticles have a range of unlimited pharmaceutical applications, including drugs delivery, gene delivery, as a sensor for pathogens detection, and tissue engineering. Various green approaches to produce nanoparticles by using living entities have been reported, such as plant extracts, fungi, yeast, actinomycetes, algae, bacteria, and viruses (Zhang et al, 2020). One such popular approach is using bacteria as a cell factory to produce the AgNPs extracellularly. To producing biocompatible NPs, bacteria-mediated synthesis is low-cost, environmentally friendly, safe, and simple (Xu et al, 2020; Ssekatawa et al, 2021)

Methods

Results

Conclusion