Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 14 4 2022 08 14 518 528 Aram Al-Soub Department of Biological Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan Khaled Khleifat Department of Medical Laboratory Sciences, Faculty of Allied Medical Sciences, Al-Ahliyya Amman University, Amman, Jordan Amjad Al-Tarawneh rince Faisal Center for Dead Sea, Environmental and Energy Research, Mutah University, Mutah, Karak, Jordan Muhamad Al-Limoun Department of Biological Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan Ibrahim Alfarrayeh Department of Biological Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan Ahmad Al Sarayreh Department of Biological Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan Yaseen Al Qaisi Department of Biological Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan Haitham Qaralleh Department of Medical Laboratory Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan Moath Alqaraleh Pharmacological and Diagnostic Research Center (PDRC), Faculty of Pharmacy, Al-Ahliyya Amman University, Amman, Jordan Anas Albashaireh Department of Biological Sciences, Faculty of Science, Mutah University, Al-Karak, Jordan 2022 03 07 2022 05 30 Background and Objectives: Nanoscience is one of the most important branches of modern science, which deals with the knowledge, structure, and properties of nanoparticles. This study aimed to investigate the ability of an airborne fungus (Aspergillus flavus) to synthesize silver nanoparticles (AgNPs) and to test the antibacterial activity of the synthesized AgNPs. Materials and Methods: The confirmation of AgNPs synthesis and the characterization of their properties were done using UV-Vis spectrophotometer, Zeta potential, Zeta sizer, FT-IR, and XRD analyses. The antibacterial activity was determined using broth microdilution method. Results: The findings showed that the average diameter of the resultant AgNPs was 474.2 nm with a PDI value of 0.27, and the zeta potential was -33.8 mV. Transmission electron microscopy (TEM) revealed that the AgNPs were regular and spherical in shape. TEM micrographs demonstrated that the AgNPs were smaller than those that were observed by DLS examination because the drying process resulted in particle shrinkage. The average size of AgNPs were less than 35 nm. The AgNPs exhibited a remarkable antibacterial activity against K. pneumoniae, E. coli, E. cloacae, S. aureus, S. epidermidis, and Shigella sp., and the MIC values ranged from 25 to 100 µg/mL. However, an exception was P. aeruginosa in which its MIC was >125 µg/mL. Conclusion: The results suggest that, the biosynthesized AgNPs by A. flavus could be utilized as a source of potent antibacterial agents in medicine and biotechnological applications. https://ijm.tums.ac.ir/index.php/ijm/article/view/3589 https://ijm.tums.ac.ir/index.php/ijm/article/download/3589/1486