TY - JOUR AU - Nour El-Dein, Mahmoud M. AU - Baka, Zakaria A. M. AU - Abou-Dobara, M. I. AU - El-Sayed, Ahmed K.A. AU - El-Zahed, Mohamed Marzouk PY - 2021/02/01 Y2 - 2024/03/29 TI - EXTRACELLULAR BIOSYNTHESIS, OPTIMIZATION, CHARACTERIZATION AND ANTIMICROBIAL POTENTIAL OF ESCHERICHIA COLI D8 SILVER NANOPARTICLES JF - Journal of microbiology, biotechnology and food sciences JA - J microb biotech food sci VL - 10 IS - 4 SE - Microbiology DO - 10.15414/jmbfs.2021.10.4.648-656 UR - https://office2.jmbfs.org/index.php/JMBFS/article/view/2555 SP - 648-656 AB - <p>This study highlights the optimization of extracellular biosynthesis and antimicrobial efficiency of silver nanoparticles (AgNPs) using the crude metabolite of <em>Escherichia coli</em> 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<sup>-1</sup>, the stretching vibration band of aromatic and aliphatic (C-N) exist at 1392.35 and 1122.37 cm<sup>-1</sup> 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 <em>Staphylococcus aureus, E. coli, Pseudomonas aeruginosa, Alternaria alternata, Fusarium oxysporum </em>and<em> Aspergillus flavus</em>. The antimicrobial activity of AgNPs was studied by TEM. TEM micrographs showed an inhibition of <em>S. aureus</em> cell multiplication. In case of <em>F. oxysporum</em>, 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 <em>S. aureus</em> and <em>Candida albicans</em>, respectively. In addition, AgNPs showed synergy effects by their combination with fluconazole that increased fold areas especially against <em>A. niger</em>, <em>A. flavus</em> and<em> F. oxysporum</em>.</p> ER -