Question
Methicillin Resistant Staphylococcus Aureus (MRSA)
Answer
MRSA (Methicillin-Resistant Staphylococcus aureus) refers to strains of S. aureus resistant to methicillin and, by extension, essentially all beta-lactam antibiotics (penicillins, cephalosporins, carbapenems) — a major cause of hospital-acquired and community-acquired infections.
Mechanism of resistance: carries the mecA gene (on the mobile SCCmec element), encoding an altered penicillin-binding protein, PBP2a, with markedly reduced affinity for beta-lactam antibiotics, conferring resistance across the entire beta-lactam class.
Types: Hospital-acquired MRSA (HA-MRSA) — often multidrug-resistant, causes surgical site/catheter-related/ventilator-associated infections; Community-acquired MRSA (CA-MRSA) — in otherwise healthy individuals, typically skin/soft-tissue infections, often carries the Panton-Valentine leukocidin (PVL) toxin gene.
Laboratory detection: cefoxitin disc diffusion testing; PCR for mecA.
Treatment: vancomycin (mainstay for serious infections), linezolid, daptomycin, or clindamycin/co-trimoxazole for less severe infections.
Infection control: contact precautions, hand hygiene, and screening of high-risk patients are essential to prevent nosocomial spread.