A superbug's resistance secret has been uncovered by scientists, paving the way for new drugs to fight infections.
For the first time, researchers have discovered how a key protein helps MRSA bacteria to evade antibiotics.
The Cfr protein acts on the ribosome, a molecular "factory" in cells responsible for making proteins that are vital for survival. Many antibiotics bind on the ribosome in bacteria and stop it functioning.
Through a chemical process called methylation, Cfr blocks the binding of antibiotics to the ribosome. At the same time it helps to keep the machinery working. In the case of MRSA, the introduction of Cfr makes the superbug resistant to seven classes of antibiotics.
Cfr is made by a mobile gene that can move easily between different species of bacteria.
Scientists found that it passed from Staphylococcus sciuri, which normally only infects animals, to the human bug Staphylococcus aureus.
S. aureus commonly lives in the nose and on the skin without causing harm. But it can be highly dangerous when it mutates into MRSA.
Lead scientist Dr Squire Booker, from Pennsylvania State University, said: "Because we know the specific mechanism by which bacterial cells evade several classes of antibiotics, we can begin to think about how to disrupt the process so that standard antibiotics can do their jobs."