MRSA stands for meticillin-resistant Staphylococcus aureus. It's a type of bacteria, and is sometimes known as a superbug. There are various strains (subtypes) of S. aureus and some strains are classed as MRSA. Strains of MRSA are very similar to any other strain of S. aureus. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most successful modern pathogens. The same organism that lives as a commensal and is transmitted in both health-care and community settings is also a leading cause of bacteraemia, ... MRSA is a contagious, antibiotic-resistant staph infection that can become dangerous. Find out the causes and symptoms, and when to call your doctor. MRSA is an infection that is resistant to certain antibiotics, including penicillin, which makes it challenging to treat. Find out what it is and why it causes concern.