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, <i>Enterococcus faecalis</i> 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 <i>vB_EfaS_LOK1</i>, isolated from urban sewage using <i>E. faecalis</i> strain IIH-74.4 as the host. Transmission electron microscopy revealed morphological features consistent with the phages formerly classified within the <i>Siphoviridae</i> 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, <i>vB_EfaS_LOK1</i> 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 <i>Efquatrovirus</i> (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 <i>vB_EfaS_LOK1</i> as a potential candidate for the development of phage-based therapies targeting <i>E. faecalis</i>.