Antibacterial potential of five phages in controlling Enterococcus faecalis and Enterococcus faecium

Enterococcus faecium and Enterococcus faecalis are opportunistic pathogens that form an increasing concern for hospital-acquired infections due to their natural and acquired antimicrobial resistance (AMR). Although phage therapy has gained global interest as a response to emerging AMR, Enterococcus remains an understudied target for phage therapy. In this context, we aimed to isolate Enterococcus-specific phages and study their in vitro infection efficacy when combined into cocktails, in the presence of antibiotics and human serum and against bacterial biofilms.

We isolated one E. faecium-phage fHoEfm07, that did not resemble any known phage genera and four E. faecalis-phages belonging to Saphexavirus (fHoEfa01 and fHoEfa06) and Efquatrovirus (fHoEfa03 and fHoEfa04) genera. The phages from the genus Saphexavirus and fHoEfm07 were suitable for therapeutic applications based on their genome characterization; however, the phages belonging to the Efquatrovirus genus contained a potential AMR-related gene. In vitro studies indicated that interactions between phages, antibiotics, and human serum depended on the specific phage-host pairing or antibiotic concentration. Moreover, only phage fHoEfa03 reduced the biofilm masses after 3 h and 24 h phage treatment.

This study provides valuable insights into the potential of Enterococcus phages in conditions mimicking phage therapy. The characterization of novel phages, assessment of their therapeutic suitability, and exploration of synergistic treatment strategies contribute to the foundational knowledge required to advance phage therapy.