Clinical meaning
Methicillin-resistant Staphylococcus aureus (MRSA) is a strain of Staphylococcus aureus that has acquired resistance to methicillin and all other beta-lactam antibiotics (penicillins, cephalosporins, and carbapenems) through the acquisition of the mecA gene. This gene encodes an altered penicillin-binding protein (PBP2a or PBP2') that has low affinity for beta-lactam antibiotics, rendering these drugs ineffective at inhibiting bacterial cell wall synthesis. Staphylococcus aureus is a gram-positive coccus that normally colonizes the skin and nares (anterior nostrils) of approximately 30% of the general population; MRSA colonizes approximately 2-5% of the population. The distinction between colonization and infection is clinically critical: colonization means the organism is present on the body without causing disease, while infection means the organism has invaded tissue and is causing an inflammatory response with clinical signs and symptoms. MRSA infections are categorized as either community-acquired (CA-MRSA) or hospital-acquired (HA-MRSA), and these categories differ in their epidemiology, virulence factors, and antibiotic susceptibility patterns. CA-MRSA typically affects young, healthy individuals and most commonly presents as skin and soft tissue infections (SSTIs): boils, abscesses, carbuncles, and cellulitis. CA-MRSA strains frequently carry the Panton-Valentine...