ORIGINAL RESEARCH article
Front. Microbiol.
Sec. Phage Biology
This article is part of the Research TopicHarnessing Bacteriophages and Phage-Engineered Products for Antibacterial and Anticancer Therapies: Challenges and OpportunitiesView all 11 articles
Characterization of Wastewater-Derived Bacteriophages Infecting Enterococcus faecalis in Bulgaria: Insights into the Novel Phage vB_SEF_8
Provisionally accepted
Yoana Krasimirova Kizheva1*
Tsveta Hristova Dimova1
Maria Ilieva Pandova1Yoana Konstantinova Gladicheva1Ralitsa Nikolaeva Petrova1
Tsvetelina Sashkova Paunova-Krasteva2
Zoltan Lubomirov Urshev3Sergei Veselinov Ivanov4Petya Koycheva Hristova1- 1Sofia University "St. Kliment Ohridski", Faculty of Biology, Sofia, Bulgaria
- 2Institut po mikrobiologia Stefan Angelov B'lgarska akademia na naukite, Sofia, Bulgaria
- 3LB Bulgaricum Plc., RnD Deparment, Sofia, Bulgaria
- 4Sofia University "St. Kliment Ohridski", Research group: Microbiological risks in the environment, Sofia, Bulgaria
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Enterococcus faecalis is an opportunistic pathogen associated with nosocomial infections, food spoilage, and reduced efficacy of orally administered medications in patients with Parkinson’s disease. Its genetic adaptability, particularly in acquiring virulence and antibiotic resistance genes, poses a significant challenge in treatment. Тhus, the development of new and effective approaches, such as phage therapy, is crucial in the fight against E. faecalis. The main goal of this study was to establish the biological characteristics of three bacteriophages (designated as vB_SEF_8, vB_SEF_13 and vB_SEF_15) isolated from wastewater in Bulgaria and their potential to eliminate E. faecalis. The host ranges of the phages were determined primarily using E. faecalis strains (n = 29), although other species within the genus Enterococcus were also included. All three phages targeted only E. faecalis strains, including antibiotic-resistant or multidrug-resistant strains. The phages showed broad pH (4.0–10.5) and temperature (up to 80 °C) stability, formed clear plaques, with maximal titers reached at various MOIs. After 9 months at 4 °C, only a slight titer reduction was observed (up to 2 log10 PFU/mL). RFLP analysis revealed genetic diversity among the three phage isolates. The phage with the broadest host range (vB_SEF_8) was characterized in more details. TEM observation revealed elongated head and long noncontractile tail. vB_SEF_8 possessed linear dsDNA and lacked genes associated with lysogeny, antibiotic resistance, or virulence. Phylogenetic analysis and the calculated pairwise intergenomic distance showed that vB_SEF_8 is a novel species within the Saphexavirus genus, class Caudoviricetes. The phage also successfully inhibited E. faecalis in a milk-based matrix. The collected data demonstrate that vB_SEF_8 holds significant potential as an antibacterial and therapeutic agent against E. faecalis in settings where the presence of this bacterium is undesirable.
Keywords: antibiotic resistance, Enterococcus faecalis, Food Safety, phage therapy, Saphexavirus phages, wastewater
Received: 28 Jul 2025; Accepted: 24 Nov 2025.
Copyright: © 2025 Kizheva, Dimova, Pandova, Gladicheva, Petrova, Paunova-Krasteva, Urshev, Ivanov and Hristova. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Yoana Krasimirova Kizheva
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