Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 14 5 2022 10 22 712 720 EN Zeinab Rezaei Department of Microbiology, Faculty of Biological Sciences, Alzahra University, Tehran, Iran Ameneh Elikaei Department of Microbiology, Faculty of Biological Sciences, Alzahra University, Tehran, Iran Seyed Mahmoud Barzi Department of Bacteriology, Pasteur Institute of Iran, Tehran, Iran Morvarid Shafiei Department of Bacteriology, Pasteur Institute of Iran, Tehran, Iran 2022 07 02 2022 09 02 Background and Objectives: Phage therapy has gained interest as an alternative treatment for methicillin-resistant Staphylococcus aureus (MRSA) infections. The purpose of this study was to isolate and characterize an effective bacteriophage against isolates of MRSA. Materials and Methods: Bacteriophage was isolated from hospital sewage. Lytic activity and the titers of phage lysates were measured using spot test and double-layer plaque assay. The phage characterization was determined through transmission electron microscopy. Adsorption rate, host range and stability tests were investigated. The latent period and burst size were estimated from a one-step growth curve. The effect of bacteriophage against MRSA biofilms was determined and Real-time PCR was used to assess the effects of the bacteriophage on the expression of the biofilm-associated genes. Results: TEM results showed that the phage resembled the Cystoviridae family. Its latent period was 30 min, corresponding to about 71/43 phage particles per infected cell. The phage had a broad host range and it was most stable at 37°C and pH 7. It was sensitive to NaCl concentrations. The expressions of the biofilm-associated genes were significantly reduced in the presence of the phage. Conclusion: The isolated phage was effective against MRSA strains and it can be an optional strategy of controlling biofilm development. https://ijm.tums.ac.ir/index.php/ijm/article/view/3795 https://ijm.tums.ac.ir/index.php/ijm/article/download/3795/1510