Methicillin Resistant Staphylococcus Aureus (MRSA) Make an Appointment Find a Doctor Ask a Question Reviewed by LeeAnn Bryant, MHS, RN, CIC (October 01, 2016) What is Staphylococcus aureus (S. aureus)? Staphylococcus aureus is a common bacterium (germ). It is present on the skin and in the nose of many people. For most healthy people this bacterium does not cause a problem. It can enter the body and cause infection. Staphylococcus aureus is most likely to enter the body if: There is an open wound in the skin The person has a suppressed immune system. S. aureus can cause serious infections of skin, bloodstream, bone, lung and other sites. What is MRSA? MRSA stands for Methicillin-Resistant Staphylococcus aureus. This is a type of S. aureus that is resistant to some of the antibiotics that are often used to treat these infections. MRSA has become increasingly common. MRSA was initially found mostly in hospitals, but now is also found in the community. People are more likely to get a MRSA infection if they: Have other health conditions Have been in the hospital or a nursing home Have been treated with antibiotics. What is the difference between colonization and infection? Colonization means MRSA is present in or on the body but is not causing illness. Healthy people may carry MRSA without becoming ill. Infection means MRSA is present in or on the body and is causing illness. Symptoms of MRSA may vary depending on the part of the body that is infected. Programs & Services Immune Deficiency Program Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.