Biological characteristics and genome analysis of Enterococcus faecalis phage vB_EfS_L1

This study focuses on the isolation, identification, and characterization of Enterococcus faecalis strain Ef-01 and the bacteriophage vB_EfS_L1 targeting it. E. faecalis was isolated from hospital laboratory samples and confirmed through PCR analysis, yielding a 1466 bp sequence with high homology to E. faecalis ATCC 19433. Antibiotic sensitivity testing revealed that Ef-01 was susceptible to six antibiotics including ciprofloxacin and linezolid, intermediately susceptible to four, and resistant to five antibiotics such as penicillin and cefradine. Subsequently, bacteriophage vB_EfS_L1 was isolated from hospital wastewater and purified through multiple rounds of plaque purification. The highest titer, reaching 4.0 × 10¹¹ PFU/mL, was achieved when propagation was carried out at a multiplicity of infection (MOI) of 0.01. Host range analysis revealed that phage vB_EfS_L1 lysed 40% of clinical Enterococcus isolates, including multidrug-resistant strains, demonstrating a moderate yet clinically relevant tropism. Further analysis showed that vB_EfS_L1 exhibited excellent stability at temperatures from -20 to 37 °C, but was inactivated at 80 °C. It also maintained activity across a pH range of 4-10, with the highest activity at acidic pH values. The bacteriophage displayed resistance to chloroform and ether but was sensitive to SDS and proteinase K. Additionally, the bacteriophage was UV-sensitive, with a rapid decline in titer upon prolonged exposure. The genome of vB_EfS_L1, consisting of 41.151 bp, was analyzed, revealing genes related to structural components, DNA replication, host lysis, and packaging. Functional gene predictions confirmed the absence of lysogeny or virulence-associated genes, ensuring the safety of vB_EfS_L1 for potential therapeutic applications. These findings highlight the bacteriophage's potential as a therapeutic agent against E. faecalis, contributing to the development of phage-based interventions in bacterial infections.