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

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.

Comparative Antimicrobial Activity of Silver Nanoparticles Obtained by Wet Chemical Reduction and Solvothermal Methods

“…Pal et al [ 60 ] showed as the truncated shapes proven a better antibacterial efficacy than the spherical nanoparticles shapes because these edges can generate damages of the cell walls. Based on the information obtained from UV-VIS results the obtained nanoparticles might possibly register an antimicrobial activity due to their shape [ 27 ] but the polydispersity indicate by the shape of graphic could affect the antimicrobial effect [ 61 , 62 ]…”

“…Probably, a higher or lesser added quantity of the reducing agent lead in time, to the various morphologies and sizes with agglomeration tendency. According to the information received from DLS results the polydispersity of the obtained nanoparticles could affect the antimicrobial activity [ 27 , 61 , 62 ].…”

“…Probably, the temperature and time of during synthesis drive to a uniform morphology but sizes of nanoparticles and agglomeration tendency are higher comparing with samples obtained at room temperature. Different syntheses routes to obtain AgNPs with antimicrobial activity lead to various results depending the reaction condition [ 61 ].…”

Antibacterial Effect of Silver Nanoparticles Is Stronger If the Production Host and the Targeted Pathogen Are Closely Related

“…UV-Vis, SEM, TEM, AFM, DLS, FTIR, ICPMS, and TGA studies were done as reported before [19]. For UV-Vis, SEM, TEM, AFM, DLS, and ICPMS, aqueous solutions of nanoparticles were used.…”

“…Comparatively, control cells show intact cells without disturbance at different scales. EDX and elemental mapping results indicated that the damage happened due to the presence of silver elements and represent a clear and sharp peak of silver [19].…”