Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 13 5 2021 10 08 691 702 Forough Goodarzi Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Masoumeh Hallajzadeh Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Mohammad Sholeh Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Malihe Talebi Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Vahid Pirhajati Mahabadi Neuroscience Research Center, Iran University of Medical Sciences, Tehran, Iran; Cellular and Molecular Research Center, Iran University of Medical Sciences, Tehran, Iran Nour Amirmozafari Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran 2021 02 16 2021 08 10 Background and Objectives: An important leading cause of the emergence of vancomycin-resistant enterococci, especially Enterococcus faecium, is the inefficiency of antibiotics in the elimination of drug-resistant pathogens. Consequently, the need for alternative treatments is more necessary than ever. Materials and Methods: A highly effective bacteriophage against vancomycin-resistant E. faecium called vB-EfmS-S2 was isolated from hospital sewage. The biological properties of phage S2 and its effect on biofilm structures were determined. Results: Phage S2 was specifically capable of lysing a wide range of clinical E. faecium isolates. According to Electron microscopy observations, the phage S2 belonged to the Siphoviridea family. Suitable pH spectra for phage survival was 5-11, at which the phage showed 100% activity. The optimal temperature for phage growth was 30-45°C, with the highest growth at 37°C. Based on one-step growth curve results, the latent period of phage S2 was 14 min with a burst size of 200 PFU/ml. The phage S2 was also able to tolerate bile at concentrations of 1 and 2% and required Mg2+ for an effective infection cycle. Biofilms were significantly inhibited and disrupted in the presence of the phage. Conclusion: According to the results, phage S2 could potentially be an alternative for the elimination and control of vancomycin-resistant E. faecium biofilm. https://ijm.tums.ac.ir/index.php/ijm/article/view/2986 https://ijm.tums.ac.ir/index.php/ijm/article/download/2986/1394