methicillin-resistant Staphylococcus aureus

Colorized scanning electron micrograph of a human neutrophil ingesting MRSA Methicillin-resistant Staphylococcus aureus (MRSA) is a group of Staphylococcus aureus strains that are resistant to β-lactam antibiotics. The β-lactam group is a broad-spectrum group of antibiotics that includes several widely used drugs, including methicillin, oxacillin, and cephalosporins. Therefore, MRSA is responsible for several difficult-to-treat infections in humans. It caused more than 100,000 deaths worldwide attributable to antimicrobial resistance in 2019. Strains unable to resist these antibiotics are classified as methicillin-susceptible S. aureus, or MSSA.

MRSA infection is common in hospitals, prisons, and nursing homes, where people with open wounds, invasive devices such as catheters, and weakened immune systems are at greater risk of healthcare-associated infection. MRSA began as a hospital-acquired infection but has become community-acquired, as well as livestock-acquired. The terms HA-MRSA (healthcare-associated or hospital-acquired MRSA), CA-MRSA (community-associated MRSA), and LA-MRSA (livestock-associated MRSA) reflect this.