Enterococcus faecium Bacteriophage vB_EfaH_163, a New Member of the Herelleviridae Family, Reduces the Mortality Associated with an E. faecium vanR Clinical Isolate in a Galleria mellonella Animal Model

Abstract

The rise of antimicrobial resistant (AMR) bacteria is a major health concern, especially with regard to members of the ESKAPE group, to which vancomycin-resistant (VRE) Enterococcus faecium belongs. Phage therapy has emerged as a novel alternative for the treatment of AMR infections. This, however, relies on the isolation and characterisation of a large collection of phages. This work describes the exploration of human faeces as a source of new E. faecium-infecting phages. Phage vB_EfaH_163 was isolated and characterised at the microbiological, genomic, and functional levels. vB_EfaH_163 phage, a new member of Herelleviridae, subfamily Brockvirinae, has a dsDNA genome of 150,836 bp that does not harbour any virulence factors or antibiotic resistance genes. It infects a wide range of E. faecium strains of different origins, including VRE strains. Interestingly, it can also infect Enterococcus faecalis strains, even some that are linezolid-resistant. Its capacity to control the growth of a clinical VRE isolate was shown in broth culture and in a Galleria mellonella animal model. The discovery and characterisation of vB_EfaH_163 increases the number of phages that might be used therapeutically against AMR bacteria.

Bacteriolytic Potential of Enterococcus Phage iF6 Isolated from “Sextaphag®” Therapeutic Phage Cocktail and Properties of Its Endolysins, Gp82 and Gp84

“…The chromosome of iF6 is a dsDNA molecule with a length of 156,592 bp and two direct terminal repeats of 2108 bp each ( Figure 5 and Figure 8 c). Similar organization of both virions and genomes has been described in phages infecting enterococci [ 38 , 39 , 40 , 41 , 42 , 43 ].…”

“…According to the phylogenetic analysis, the most closely related phage to iF6 is Enterococcus phage 163 (vB_EfmH_163) [ 42 ] ( Figure 6 ). The vB_EfmH_163 and iF6 phages have 86% whole-genome identity ( Supplementary Information, Table S4 ).…”

“…The vB_EfmH_163 phage is stable in pH ranging from 2 to 9, while iF6 has a narrow range of pH stability (near pH 7) ( Figure 2 b). The difference in the pH stability of the phages may be related to the conditions under which the experiments were carried out, in particular, PBS buffers with pH 2–9, in which the vB_EfmH_163 phage was incubated [ 42 ].…”

“…The average burst size of iF6 was 31 ± 1 PFU per infected cell, while the latent period was about 60 min, and the duration of the rise period was 30 min ( Figure 5 b). Of all representatives of Shiekvirus and Kochikohdavirus , bacteriophages have the largest progeny: vB_EfmH_163 (155 PFU per infected cell [ 42 ]), phiEF24C (110-120 PFU per infected cell [ 38 ]), and EfV12-phi1 (135 PFU per infected cell [ 44 ]), notwithstanding the tiny dimensions of their plaques—only about 0.3 mm in diameter [ 44 , 45 ]. The limited burst size of enterococcal phages belonging to these two genera can be explained by the large size of their virions (~0.285 µm from the top of the head to the baseplate), and the small size of the host cells (~0.8 µm) [ 46 ].…”

“…The EF1TV phage was able to eradicate biofilms formed by clinical isolates of E. faecalis [ 47 ]. The vB_EfmH_163 phage reduced mortality caused by infection with an E. faecium vanR clinical isolate in a Galleria mellonella animal model [ 42 ]. Thus, iF6, as well as other members of Schiekvirus and Kochikohdavirus , can be used as antibacterial agents against antibiotic-resistant enterococci infections.…”