Characterization and genome analysis of novel phage vB_EfaP_IME195 infecting Enterococcus faecalis

Abstract

Enterococcus faecalis is one of the main bacteria in the human and animal intestine but is also classed as an opportunistic pathogen. During normal growth, E. faecalis produces natural antibiotics and is conducive to human health. As ectopic parasites, E. faecalis is capable of causing infective endocarditis, neonatal sepsis, bloodstream infections, bacteremia, and intraabdominal infections. With the incidence of antibiotic resistance reaching crisis point, it is imperative to find alternative treatments for multidrug-resistant infections. Using phage for pathogen control is a promising treatment option to combat bacterial resistance. In this study, a lytic phage, designated vB_EfaP_IME195, was isolated from hospital sewage using a clinical multidrug-resistant Enterococcus faecalis strain as an indicator. The one-step growth curve with the optimal multiplicity of infection of (MOI) 0.01 revealed a latent period of ~ 30 min and a burst size of ~ 120 plaque-forming units (pfu) per cell. Transmission electron microscopy showed that the phage belongs to the family Podoviridae. Phage vB_EfaP_IME195 has a linear, double-stranded DNA genome of 18,607 bp with a G + C content of 33% and 27 coding sequences (GenBank accession no. KT932700). Run-off sequencing experiments showed that the phage has a unique 59-bp inverted repeat sequences at the terminal ends. BLASTn analysis revealed that vB_EfaP_IME195 shares 92% identity (93% genome coverage) with unpublished E. faecalis phage Idefix. This study reported a novel E. faecalis phage with unique genome termini containing inverted repeats. The isolation and characterization of this novel lytic E. faecalis phage provides the basis for the development of new therapeutic agents like phage cocktails for multidrug-resistant E. faecalis infection, and its unique genomic feature would also provide valuable knowledge and insight for further phage genome analysis.