Biological Characteristics and Genomic Analysis of the Novel Bacteriophage Enterococcus faecium vB_EfaP_2/Chl-5

Enterococcus faecium, a gram-positive commensal of the gastrointestinal tract, has evolved into a dangerous pathogenic microorganism characterized by ecological plasticity, rapid emergence of antibiotic-resistant strains, and biofilm-forming ability. In the context of the antibiotic resistance crisis, the search for new lytic phages represents a critically important therapeutic alternative. In this study, a novel lytic phage, vB_EfaP_2/Chl-5, was isolated from a bronchoalveolar lavage sample obtained from a patient in a chronic critical condition. Analysis of electron microscopy data and full-genome sequence showed that phage vB_EfaP_2/Chl-5 belongs to the Salasmaviridae family and has the podovirus morphotype. Based on the data from a single-step growth experiment, it was determined that the latent period of phage vB_EfaP_2/Chl-5 is approximately 40 min, and the phage yield is 68 plaque-forming units per cell. It was found that 70% of viral particles are adsorbed on the host cells within 5 min. The maximum phage yield is achieved at multiplicity of infection equal to 1. High infection productivity was confirmed for 26% of E. faecium isolates of various origin (n = 14) based on the efficiency of plating (≥0.5). The bacteriophage showed high thermal stability in the range from –70 to 60°C and retained infectious activity at pH 4.0 to 10.0, as well as in the presence of 5% NaCl. Genomic analysis of phage vB_EfaP_2/Chl-5 showed that the phage genome consists of double-stranded DNA, 18 099 base pairs in length and encodes 27 open reading frames. In the genome there are no genes of antimicrobial resistance, virulence, and lysogeny. Furthermore, phage vB_EfaP_2/Chl-5 effectively targets biofilms in vitro, reducing the number of viable cells. The results indicate the high potential of vB_EfaP_2/Chl-5 for treating infections caused by E. faecium.