What is Staphylococcus aureus, and what is MRSA?

Staph is a type of bacteria. It may cause skin infections that look like pimples or boils. Skin infections caused by Staph may be red, swollen, painful, or have pus or other drainage. Some Staph (MRSA) are resistant to certain antibiotics, making it harder to treat. The information on this page applies to both Staph and MRSA.