Isolation and characterization of a novel Enterococcus faecalis bacteriophage phi EF24C as a therapeutic candidate

Vancomycin-resistant Enterococcus faecalis (VRE) has become a significant threat in nosocomial settings. Bacteriophage (phage) therapy is frequently proposed as a potential alternative therapy for infections caused by this bacterium. To search for candidate therapeutic phages against Enterococcus faecalis infections, 30 Enterococcus faecalis phages were isolated from the environment. One of these, virulent phage phi EF24C, which has a broad host range, was selected for analysis. The plaque-forming ability of phi EF24C was virtually unaffected by differences in the clinical host strains. Furthermore, the phage had a shorter latent period and a larger burst size than ordinary tailed phages, indicating that phi EF24C has effective lytic activity against many Enterococcus faecalis strains, including VRE. Morphological and genomic analyses revealed that phi EF24C is a large myovirus (classified as family Myoviridae morphotype A1) with a linear double-stranded DNA genome of c. 143 kbp. Analyses of the N-terminal amino acid sequences of the virion proteins, together with the morphology and the genome size, speculated that phi EF24C is closely related to other myoviruses of Gram-positive bacteria that have been used experimentally or practically for therapy or prophylaxis. Considering these results, phi EF24C may be a potential candidate therapeutic phage against Enterococcus faecalis infections.