Enterococci such as Enterococcus faecalis and Enterococcus faecium are part of the normal human gut microbiota. However they can also be a source of nosocomial infections specially in immunocompromised patients. Virulent bacteriophages, i.e., viruses that infect and obligatorily lyse bacteria might provide alternative options for combating them. Yet, bacterial resistance to phage is taking place in similar fashion to antibiotic resistance. This might be, in part due to temperate phages that are stably associated with their host. They compete for their bacterial host, in addition to repressor-dependent immunity against similar phages, some phage express genes conferring resistance to infection by more or less unrelated phages. They can encode abortive infection (Abi) mechanisms that cause an interruption of invasive phage development and a premature death of the infected bacteria. For instance, E. faecalis V583 prophage 6 confers resistance to the virulent phage Idefix infection mainly due to Abia-alpha protein. This Pfam family corresponds to Abi-alpha protein sequences which is mostly found in prophages, arguing that it is essentially a temperate phage weapon to fight against other phages [1].

1: Enterococcus faecalis Countermeasures Defeat a Virulent Picovirinae Bacteriophage. Lossouarn J, Briet A, Moncaut E, Furlan S, Bouteau A, Son O, Leroy M, DuBow MS, Lecointe F, Serror P, Petit MA; Viruses. 2019; [Epub ahead of print] PMID:30634666