Methicillin-Resistant Staphylococcus Aureus (MRSA) - Overview. Methicillin-resistant Staphylococcus aureus (MRSA) is a type of staphylococcus or  staph  bacterium that is resistant to many antibiotics.Staph bacteria, like other kinds of bacteria, normally live on your skin and in your nose, usually without causing problems.ethicillin-Resistant Staphylococcus Aureus (MRSA) - Overview. Methicillin-resistant Staphylococcus aureus (MRSA) is a type of staphylococcus or  staph  bacterium that is resistant to many antibiotics.