Staphylococcus aureus is a common bacterium often found on the skin and in the nose of healthy people. This is called "colonisation" or "carriage".
Some strains of Staphylococcus aureus are resistant to certain antibiotics, particularly meticillin and are known as MRSA (Meticillicin Resistant Staphylococcus Aureus).
The majority of people who are colonised with MRSA will never get an infection. Problems only begin to occur if MRSA gets into the body through cuts or wounds, or into a part of the body that is normally sterile, such as the bladder.
For those people who are vulnerable because they are already unwell or have injuries or surgical wounds, the risk of developing an infection is higher. 

Organisms such as MRSA usually spread from person to person by direct contact. The easiest way to stop the spread is by practising good hand hygiene.

 More information on MRSA in hospital and healthcare environments