Bacteria can be infected by tiny viruses called bacteriophages (phages). Bacteriophages are so small they do not even have a single cell, but are instead just a piece of DNA surrounded by a protein coat. When they attack a bacterium, bacteriophages can multiply very quickly until the bacterium bursts and releases lots of new phages. Trillions of bacteria and bacteriophages live in and on the human body and they are vital for a normal, healthy life. We are interested in seeing if we can use phages to help doctors to treat diseases and to help people live healthy lives.