In use in Eastern Europe since the early 1900s, phages are viruses that attack bacteria. Considered as safe and reliable as aspirin over there, the FDA has reservations that make their use rare and last-ditch here.
studies published over the past several decades, based on trials conducted at Eliava and elsewhere in Eastern Europe, have shown that phage therapy has an 80 to 90 percent success rate against bacteria likely to show antibiotic resistance, such as Staphylococcus aureus and Escherichia coli. In contrast, many antibiotics fail outright against the evolved forms of these pathogens.
That's 80 - 90 % success against bacteria that we can't kill - the so-called flesh-eating bacteria.