Unlocking the Potential of vB_EfaS_LOK1: A Newly Isolated Bacteriophage Against Enterococcus faecalis

Phage therapy has emerged as a promising alternative for combating infections caused by drug-resistant pathogens. Among these, Enterococcus faecalis remains a significant public health concern due to its persistence in clinical settings and frequent involvement in healthcare-associated infections (HAIs). In this study, we report the characterization of the lytic bacteriophage vB_EfaS_LOK1, isolated from urban sewage using E. faecalis strain IIH-74.4 as the host. Transmission electron microscopy revealed morphological features consistent with the phages formerly classified within the Siphoviridae family. The phage exhibited high thermal and pH stability, remaining viable up to 70 °C and within a pH range of 4-11. It displayed a latent period of 20 min and a burst size of 72 PFU/cell. Notably, vB_EfaS_LOK1 exhibited a narrow host range, lysing only the strain used for their isolation. Genomic analysis revealed a 41.2 kb double-stranded DNA genome devoid of known virulence or antibiotic resistance genes. Phylogenomic analysis classified the phage within the genus Efquatrovirus (Caudoviricetes), suggesting it represents a newly isolated bacteriophage species. Functional annotation identified genes related to DNA replication, host interaction, and bacterial lysis, including endolysins and holins with putative antimicrobial properties. Long-term stability assays demonstrated that tryptic soy broth (TSB) with CaCl₂/MgCl₂ at 4 °C maintained viability for at least 90 days. Collectively, these findings support the potential of vB_EfaS_LOK1 as a potential candidate for the development of phage-based therapies targeting E. faecalis.