Methicillin-resistant Staphylococcus aureus (MRSA) is an isolate of the bacterium Staphylococcus aureus characterized by antibiotic resistance to all penicillins, including methicillin and other narrow-spectrum ß-lactamase-resistant penicillin antibiotics.[1] MRSA was discovered for the first time in 1961 in the UK, but it is now widespread in the hospital setting. MRSA is commonly termed a superbug.

MRSA may also be known as oxacillin-resistant Staphylococcus aureus (ORSA) and multiple-resistant Staphylococcus aureus. Strains of S. aureus that are non-resistant to methicillin are sometimes called methicillin-susceptible Staphylococcus aureus (MSSA) if an explicit distinction must be made.

Although MRSA has traditionally been seen as a hospital-associated infection, community-acquired MRSA strains have appeared in recent years, notably in the U.S. and Australia.[2] The abbreviations CA-MRSA (community-associated MRSA) and HA-MRSA (hospital-associated MRSA) are now commonly seen in medical literature.