Methicillin-resistant Staphylococcus aureus, or MRSA, is a staph bacterium transmitted through contact with a person carrying it or by touching objects contaminated with it, according to WebMD. It often enters the body through a cut or open wound and can infect the skin, bloodstream, urinary tract and lungs.
MRSA is resistant to methicillin, penicillin, amoxicillin and other common antibiotics, reports WebMD. Although some antibiotics still work against MRSA, the bacterium continually adapts and becomes resistant. As of 2015, researchers are constantly developing new medicines to battle MRSA. People with weakened immune systems residing in nursing homes, hospitals and other facilities are particularly prone to MRSA infection.