Methicillin-resistant Staphylococcus aureus (MRSA) is a strain of bacteria that has developed resistance to many commonly used antibiotics, including methicillin and related drugs. It can cause a range of infections, from mild skin infections such as boils and abscesses to more serious infections involving the bloodstream, lungs, surgical wounds, or other organs. MRSA is often categorized as community-associated or healthcare-associated, depending on where it is acquired. Symptoms vary by infection site but may include redness, swelling, pain, fever, and drainage of pus. Because MRSA is resistant to several standard antibiotics, infections can be more difficult to treat and may spread in settings where close contact or compromised immunity is present.