I think it's amazing that there are billions of bacteria living in my guts and keeping me healthy. Sometimes people's gut bacteria get out of balance and make them ill, and antibiotics don't always help.
The NHS medicines watchdog has approved a new treatment for certain infections. Doctors found that taking faecal matter (otherwise known as poo) from healthy people and transplanting it into patients' guts made almost all of them better.
Good news for healthcare... but I'm not sure I'd want somebody else's poo in my body!