Methicillin-resistant Staphylococcus aureus (MRSA) is a type of bacteria resistant to common antibiotics like methicillin, oxacillin, penicillin, and amoxicillin. MRSA infections most often occur in hospitals and healthcare facilities among people with weakened immune systems. Community-associated MRSA (CA-MRSA) infections can develop in people who have not recently been hospitalized or had a medical procedure.