Staphylococcus aureus, also known as staph, is a very common bacterium that can live on the skin or in the noses of healthy people. Methicillin-resistant Staphylococcus aureus, or MRSA, is a type of staph bacteria that cannot be treated with antibiotics called beta-lactams which include methicillin, oxacillin, penicillin, and amoxicillin. This resistance makes choosing the right antibiotic challenging. In the community, most MRSA infections are skin infections that cause skin lesions—such as pimples and boils—and are often easy to treat. MRSA in a hospital or healthcare setting can be a different strain than MRSA in the community. Resistant staph can be life-threatening to older people and those with weakened immune systems. Patients who are most at risk for serious infections are those with open wounds, burns, or tubes inserted in their bodies that provide a path for infection to be carried through the bloodstream and internal organs.