الفهرس 
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Abstract
In this study, three selected bacterial isolates were isolated from Damietta Governorate, Egypt (It was for the first time explored for the NP synthesis using bacteria). The isolates were isolated on nutrient agar medium at 37◦C for 24 hrs and they were tested for the ability of AgNPs biosynthesis. These bacterial isolates were identified according to cultural, morphological, physicochemical and molecular techniques and they were designated as Raoultella ornithinolytica EGD6, Escherichia coli D8 and Leclercia adecarboxylata EGD11. It was found that Escherichia coli D8 is the best biofactory using nitrate reductase enzyme having an activity of 2180.6 nmol/ h/ mL. Bacterial supernatants were obtained by subculturing on nutrient agar plates then were inoculated in nitrate broth medium and incubated for 24 hrs at 37◦C at a rotation rate of 150 rpm.
Optimized reaction conditions such as concentration of silver nitrate (1.75 mM for Raoultella ornithinolytica EGD6 and Escherichia coli D8 and 1.5 mM for Leclercia adecarboxylata EGD11), concentration of bacterial supernatant (35% (v/v%) for R. ornithinolytica EGD6 and E. coli D8 and 32% (v/v%) for L. adecarboxylata EGD11), temperature (35◦C) and pH value (pH 8) have produced extremely stable NPs within 72 hrs in dark conditions while the production occurred throughout minutes in the presence of solar irradiation. These NPs were characterized by UV–vis spectrophotometer, Transmission Electron Microscopy (TEM) analyses, Zeta potential analyzer and size distribution by volume. The AgNPs particular structure was detected by the analysis of colloidal solution with selected area diffraction pattern (SADP), where this pattern detected the structure of AgNPs crystals, which is a confirmation for their synthesis, the nanocolloidal solution. AgNPs stability is detected by zeta potential analyzer, the measured values are -30.9 for R. ornithinolytica EGD6, -33.6 for E. coli D8 and -31.0 for L. adecarboxylata EGD11. The previous values confirmed the higher stability of nanocolloidal solution.
In this study, the antimicrobial activity against some pathogenic bacterial and fungal strains were studied using optimized biosynthesized AgNPs by Escherichia coli D8. The highest antibacterial activity of AgNPs was recorded against Staphylococcus aureus followed by E. coli, Pseudomonas aeruginosa, MRSA, Klebsiella pneumoniae, Leclercia adecarboxylata EGD11, Bacillus cereus, E. coli D8 and Raoultella ornithinolytica EGD6. In addition to antibacterial activity, AgNPs have a superior potent toxic effect against Aspergillus niger followed by A. fumigatus, A. flavus, Alternaria alternata, Fusarium oxysporum f. sp. lycopersici and Candida albicans.
In this study, Raoultella ornithinolytica EGD6, Escherichia coli D8 and Leclercia adecarboxylata EGD11 were used as good extracellular biosynthesizing agents of new functional optimized antimicrobial AgNPs against some pathogenic human bacteria and some phytopathogenic fungi and can be used as inhibition agents against these microorganisms.