Staphylococcus aureus (Staph) bacteria are commonly carried on the skin or in the nose of healthy people. Sometimes, staph can cause an infection. Staph bacteria are one of the most common causes of skin infections. However, staph bacteria also can cause serious infections (such as surgical wound infections, bloodstream infections, and pneumonia). Staph bacteria that are resistant to many antibiotics (drugs that kill bacteria), also called methicillin-resistant Staphylococcus aureus (MRSA). Some, but not all Staph bacteria are resistant strains (MRSA). The publications page explains prevention and treatment options and other helpful information.