Superbugs resistant to emergency antibiotics are spreading in hospitals, a Europe-wide study shows.
Drugs called carbapenems are used when an infection cannot be treated with anything else.
The spread of resistant Klebsiella pneumoniae was "extremely concerning", researchers from the Sanger Institute said.
And they warned other bugs could become resistant too - because of the unique way bacteria have sex.
What is Klebsiella pneumoniae?
It can live completely naturally in the intestines without causing problems for healthy people.
However, when the body is unwell, it can infect the lungs to cause pneumonia, and the blood, cuts in the skin and the lining of the brain to cause meningitis.