Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 14 6 2022 12 06 863 873 Niloofar Sabzi Department of Microbiology, Faculty of Medicine, Kashan University of Medical Sciences, Kashan, Iran Rezvan Moniri Department of Microbiology, Faculty of Medicine, Kashan University of Medical Sciences, Kashan, Iran Mojtaba Sehat Trauma Research Center, Kashan University of Medical Sciences, Kashan, Iran Hadis Fathizadeh Student Research Committee, Sirjan School of Medical Sciences, Sirjan, Iran AND Department of Laboratory Sciences, Sirjan School of Medical Sciences, Sirjan, Iran Ali Nazari-Alam Department of Microbiology, Faculty of Medicine, Kashan University of Medical Sciences, Kashan, Iran AND Infectious Diseases Research Center, Kashan University of Medical Sciences, Kashan, Iran 2022 07 19 2022 10 27 Background and Objectives: In the past few years, application of new antimicrobial e.g. nanoparticles (NPs) to treat infection caused by drug-resistant bacteria has increased. This study aimed to determine antimicrobial property of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) in combination with linezolid on Enterococcus biofilm. Materials and Methods: A total of forty-eight isolates of Enterococcus spp. were collected and confirmed by PCR method. The synthesis of biocompatible AgNPs was performed, then analyzed by Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy. We carried out minimum inhibitory concentration (MIC) and biofilm forming capacity of AgNPs and AuNPs with linezolid. Results: Twenty-two E. faecium isolates and twenty- six E. faecalis investigated in this study. Strong biofilm formation was seen in 12 (25%) of isolates, and others isolates (75%) formed moderate biofilm. AgNPs and Au-NPs size were 26 nm and 20 nm respectively. The MIC of AgNPs was 23.2 μg/ml, and AuNPs were 92.1 μg/ml and the lowest MIC was obtained 2 μg/ml in linezolid. Biofilm formation inhibitory activity by AuNPs + Linezolide and AgNPs + Linezolide 70 to 80 percent increased in average. Conclusion: The antibiofilm activity of AgNPs and AuNPs increased when both agents were used in combination with linezolid in comparison with each agent alone. https://ijm.tums.ac.ir/index.php/ijm/article/view/3830 https://ijm.tums.ac.ir/index.php/ijm/article/download/3830/1527