Slate has an interesting article about phages. As you may remember from your high school biology classes, a bacteriophage is a virus that infects bacteria.
Before the age of modern antibiotics, phages were used to treat some bacterial infections. But once antibiotics became widely used, only countries like the former Soviet Union continued to use them. Now that antibiotic resistant strains of bacteria are becoming more common, interest in phage therapy is spreading. Indeed, it is said that there may now be bacteria that only phages can effectively treat. Thus leading to a growing flow of people to the former Soviet bloc countries for treatment. YMMV. Use at your own risk. This is not an endorsement. I am not a doctor nor do I play one on TV. Insert disclaimer here.
Aloha!