From the Mayo Clinic website....
MRSA infection is caused by Staphylococcus aureus bacteria — often called "staph." MRSA stands for methicillin-resistant Staphylococcus aureus. It's a strain of staph that's resistant to the broad-spectrum antibiotics commonly used to treat it. MRSA can be fatal.
Most MRSA infections occur in hospitals or other health care settings, such as nursing homes and dialysis centers. It's known as health care-associated MRSA, or HA-MRSA. Older adults and people with weakened immune systems are at most risk of HA-MRSA. More recently, another type of MRSA has occurred among otherwise healthy people in the wider community. This form, community-associated MRSA, or CA-MRSA, is responsible for serious skin and soft tissue infections and for a serious form of pneumonia
Staph skin infections, including MRSA, generally start as small red bumps that resemble pimples, boils or spider bites. These can quickly turn into deep, painful abscesses that require surgical draining. Sometimes the bacteria remain confined to the skin. But they can also penetrate into the body, causing potentially life-threatening infections in bones, joints, surgical wounds, the bloodstream, heart valves and lungs
MRSA is a strain of staph that's resistant to the broad-spectrum antibiotics commonly used to treat it.
Staph infections
Staph bacteria are normally found on the skin or in the nose of about one-third of the population. If you have staph on your skin or in your nose but aren't sick, you are said to be "colonized" but not infected. Healthy people can be colonized and have no ill effects. However, they can pass the germ to others.
Staph bacteria are generally harmless unless they enter the body through a cut or other wound, and even then they often cause only minor skin problems in healthy people. However, staph infections can cause serious illness. This most often happens in older adults and people who have weakened immune systems, usually in hospitals and long term care facilities. But in the past several years, serious infections have been occurring in otherwise healthy people in the community, for example athletes who share equipment or personal items.