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Silver nanomaterials are usually applied as antimicrobial agents; however, they can cause toxic effects on human health. The current investigation was performed to study the combined effects of chitosan and silver nanoparticles (AgNPs) using the cell-free supernatant of Escherichia coli (MF062579). The produced chitosan/silver nanocomposite (CS/AgNC) showed good antibacterial activity and high stability. The biosynthesized CS/AgNC contained homogeneous spherical AgNPs with an average size of ~12.3 nm and a net surface charge of +30.9 ± 3.2 mV. CS/AgNC revealed a good minimum inhibitory concentration (MIC) result against Gram-negative (G-ve, E. coli) and Gram-positive (G+ve, Bacillus cereus) bacteria with inhibition ratios of 80.7% and 75.5%, respectively. Nanocomposite-treated cells displayed complete lysis of the bacterial cell, a low amount of DNA, and cell membrane and wall disruption. Glutamate dehydrogenase (GDH) and malate dehydrogenase (MDH) activities of tested bacterial strains were demonstrated using spectrophotometry and electrophoresis on a non-denaturing acrylamide gel. In CS/AgNC-treated strains, enzyme production and activity were fewer than in untreated strains. The obtained results suggested that CS/AgNC seems to be more effective against G-ve than G+ve bacteria. [ABSTRACT FROM AUTHOR]

Conventional antifungal agents have failed to treat several infectious diseases of many Aspergillus strains. These strains have been linked to the production of high-potency mycotoxins, which cause mould diseases on fruits and vegetables and have negative health consequences. The current study aimed to develop new effective nanomaterials using efficient methods that were stable and antifungal. The current work has been carried out to use the free cell supernatant of Escherichia coli D8 (MF062579) in the biosynthesis of reduced graphene oxide/silver nanocomposite (rGO/AgNC). At room temperature, the nanocomposite was prepared by an economical and simple one-step approach. Different parameters were optimized in the biofabrication of rGO/AgNC such as silver nitrate concentration, bacterial supernatant concentration, pH value, and temperature. Ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Zeta analyses were used to evaluate the optimized rGO/AgNC. The biosynthesis process was performed within minutes in the incidence of solar irradiation. The mean size of silver nanoparticles (AgNPs) was estimated to be 9-18 nm. The biogenesis of spherical-shaped, well-dispersed AgNPs was validated by TEM images. AgNPs have a positive potential value, as seen by the zeta potential graph. rGO/AgNC had a harmful effect on the ultrastructure of rGO/AgNC-treated Aspergillus including membranes damage, malformation, and complete lysis of fungal cells in addition to enzymatic inhibition in lactate dehydrogenase activity. This study states a well-designed approach to develop a new antimicrobial agent, rGO/AgNC, against pathogenic human and phytopathogenic Aspergillus spp. in addition to a probable mechanism for the nanomaterial’s antimicrobial action. [ABSTRACT FROM AUTHOR]

Central composite design (CCD) as one of response surface designs was employed to optimize the biosynthesis process of silver nanoparticles (AgNPs). In this design, fungal cell-free filtrate of Talaromyces stipitatus was applied as a biosource for the biosynthesis of AgNPs. Different variables with five levels were used to optimize AgNPs biosynthesis. Independent variables were concentration of silver nitrate (AgNO3; mmole), temperature (°C), time, pH and ratio of AgNO3 to cell free extract. While dependent variable was peak intensity of surface plasmon resonance (SPR) at wavelength 420 nm. The predicted optimal setup parameters were AgNO3 concentration of 7 mmol, temperature of 25 °C, time of 91.2 hr, pH of 8 and ratio of AgNO3 solution to cell-free extract of 2:1. The characteristics of biosynthesized AgNPs were revealed using Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), zeta potential, energy dispersive x-ray analysis (EDX), and transmission electron microscopy (TEM). Biosynthesized AgNPs appeared to be spherical, with mean size of 13.95 nm and zeta potential of 9.85 mV. Biosynthesized AgNPs were also examined for their antimicrobial properties against selected bacterial and fungal pathogens including Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Aspergillus flavus, A. niger, Fusarium oxysporum and Alternaria alternata. [ABSTRACT FROM AUTHOR]

A novel biosynthesis of dual reduced graphene oxide/silver nanocomposites (rGO/AgNC) using the crude metabolite of Escherichia coli D8 (MF06257) strain and sunlight is introduced in this work. Physicochemical analysis of these rGO/AgNC revealed that they are sheet-like structures having spherically shaped silver nanoparticles (AgNPs) with an average particle size of 8 to 17 nm, and their absorption peak ranged from 350 to 450 nm. The biosynthesized rGO/AgNC were characterized by UV–vis and FT-IR spectra, X-ray diffraction, Zeta potential and transmission electron microscopy. After the injection of these nanocomposites to mice, their uptake by the kidney and liver has been proven by the ultrastructural observation and estimation of the hepatic and renal silver content. These nanocomposites caused a moderate toxicity for both organs. Changes in the liver and kidney functions and histopathological effects had been observed. The rGO/AgNC revealed a remarkable antitumor effect. They showed a dose-dependent cytotoxic effect on Ehrlich ascites carcinoma (EAC) cells in vitro. Treatment of mice bearing EAC tumors intraperitoneally with 10 mg/kg rGO/AgNC showed an antiproliferative effect on EAC cells, reduced ascites volume, and maintained mice survival. The results indicate that this green synergy of silver nanoparticles with reduced graphene oxide may have a promising potential in cancer therapy. [ABSTRACT FROM AUTHOR]

This study highlights the optimization of extracellular biosynthesis and antimicrobial efficiency of silver nanoparticles (AgNPs) using the crude metabolite of Escherichia coli D8 (MF06257) strain. The bacterial strain had been isolated from a sewage water stream located in Damietta City, Egypt. The optimum conditions for AgNPs production were at temperature 35°C, pH 7 and 1.5mM silver nitrate. The AgNPs biosynthesis was detected in culture filtrate within 1-2 minutes at room temperature (25±2°C) and sunlight. The characterization of AgNPs was studied by UV-Vis spectroscopy (maximum absorbance at 429 nm), X-ray diffraction (XRD) pattern (crystal planes were 110, 111, 200, 211, 220, and 311), transmission electron microscopy (TEM) (AgNPs were spherical in shape ranging from 6 to 17 nm), Fourier transform-infrared (FTIR) spectroscopy (the bands of symmetric and asymmetric amines were assigned at 3421.1 and 2962.13 cm-1, the stretching vibration band of aromatic and aliphatic (C-N) exist at 1392.35 and 1122.37 cm-1 bands), Zeta potential analyser (AgNPs had a negative charge value; -33.6 mV) and size distribution by volume (the presence of capping agent enveloping the AgNPs with a mean size of 136.0-294.3 nm). Nitrate reductase (NR) was assayed as an important partner in the optimized production (the rate of NR reached to 2.18 U/ml). The study demonstrated that AgNPs are potent inhibitors of Staphylococcus aureus, E. coli, Pseudomonas aeruginosa, Alternaria alternata, Fusarium oxysporum and Aspergillus flavus. The antimicrobial activity of AgNPs was studied by TEM. TEM micrographs showed an inhibition of S. aureus cell multiplication. In case of F. oxysporum, a reduction in the size of treated cells, formation of a mucilage matrix connecting the hyphal cells together, the appearance of a big vacuole, lipid droplets an a severe leakage of cytoplasmic contents were detected. AgNPs exhibited MIC values of 6.25μg/ml and 50 μg/ml against S. aureus and Candida albicans, respectively. In addition, AgNPs showed synergy effects by their combination with fluconazole that increased fold areas especially against A. niger, A. flavus and F. oxysporum. [ABSTRACT FROM AUTHOR]