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Methicillin-resistant Staphylococcus aureus
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<p>Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) is a group of <a href="/facts/Gram-positive_bacteria/H6WYQ17e">gram-positive bacteria</a> that are genetically distinct from other <a href="/facts/Strain_(biology)/xFv4QWjN">strains</a> of <i><a href="/facts/Staphylococcus_aureus/9yDVBMsc">Staphylococcus aureus</a></i>. MRSA is responsible for several difficult-to-treat <a href="/facts/Infection/182XrncP">infections</a> in humans. It caused more than 100,000 deaths worldwide attributable to <a href="/facts/Antimicrobial_resistance/jsbAywgx">antimicrobial resistance</a> in 2019. </p><p>MRSA is any strain of <i>S. aureus</i> that has developed (through <a href="/facts/Mutation/Ee4NnWbY">mutation</a>) or acquired (through <a href="/facts/Horizontal_gene_transfer/FPyUIsf2">horizontal gene transfer</a>) a <a href="/facts/Multiple_drug_resistance/TPbHtAvz">multiple drug resistance</a> to <a href="/facts/Beta-lactam_antibiotics/MTqEtwsg">beta-lactam antibiotics</a>. Beta-lactam (β-lactam) antibiotics are a <a href="/facts/Broad-spectrum_antibiotic/gITH5ecM">broad-spectrum group</a> that include some <a href="/facts/Penam/c4ncQ7HK">penams</a> (<a href="/facts/Penicillin/Abo8VQ3p">penicillin</a> derivatives such as <a href="/facts/Methicillin/nIrTI5sp">methicillin</a> and <a href="/facts/Oxacillin/rU9nGdrE">oxacillin</a>) and <a href="/facts/Cephem/2SRFx84S">cephems</a> such as the <a href="/facts/Cephalosporin/WeB7I75T">cephalosporins</a>. Strains unable to resist these antibiotics are classified as methicillin-susceptible <i>S. aureus</i>, or MSSA. </p><p>MRSA infection is common in hospitals, prisons, and nursing homes, where people with open <a href="/facts/Wound/snv0h3Gj">wounds</a>, invasive devices such as <a href="/facts/Catheter/ehnH1eF5">catheters</a>, and weakened <a href="/facts/Immune_system/HRCTf1pb">immune systems</a> are at greater risk of <a href="/facts/Hospital-acquired_infection/sKWTbPTq">healthcare-associated infection</a>. 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. </p>