Characterization of Enterococcus faecium bacteriophage IME-EFm5 and its endolysin LysEFm5

- The phage IME-EFm5 is a rare example of an Enterococcus faecium phage family.
- The lytic activity of endolysin LysEFm5 is zinc ion independent.
- LysEFm5 shows broad and high-efficient antibacterial activity against E. faecium.
- LysEFm5 might be an alternative treatment strategy for E. faecium infections.

Due to the worldwide prevalence of antibiotic resistant strains, phages therapy has been revitalized recently. In this study, an Enterococcus faecium phage named IME-EFm5 was isolated from hospital sewage. Whole genomic sequence analysis demonstrated that IME-EFm5 belong to the Siphoviridae family, and has a double-stranded genome of 42,265 bp (with a 35.51% G+C content) which contains 70 putative coding sequences. LysEFm5, the endolysin of IME-EFm5, contains an amidase domain in its N-terminal and has a wider bactericidal spectrum than its parental phage IME-EFm5, including 7 strains of vancomycin-resistant E. faecium. The mutagenesis analysis revealed that the zinc ion binding residues (H27, H132, and C140), E90, and T138 are required for the catalysis of LysEFm5. However, the antibacterial activity of LysEFm5 is zinc ion independent, which is inconsistent with most of other amidase members. The phage lysin LysEFm5 might be an alternative treatment strategy for infections caused by multidrug-resistant E. faecium.