Methicillin-resistant Staphylococcus aureus is a type of S. aureus that does not respond to some antibiotics that are used to treat traditional staph infections. MRSA has acquired resistance to penicillinase-stable penicillins such as methicillin oxacillin, and nafcillin. This resistance is mediated by a chromosomal DNA segment encoding a new penicillin binding protein that prevents β-lactam antibiotics from binding to the PBP.
MRSA frequenty has additional virulence factors, such as Pantine-Valenitine leukocidin, which increases it's virulence.
Like traditional S. aureus, MRSA commonly colonizes the nares has the potential to infect wounds, the respiratory tract, IV catheters, and the urinary tract. Many MRSA infections are nosocomial. Community-acquired MSRA is also seen in more commonly in "communal" settings such as sports teams, family clusters, etc. Immunocompromised patients are also at an increased risk of infection.
Diagnosis is based on normal cultures from blood, urine, or other samples with antimicribial sensitivity testing. However, because these tests take time to complete and early intervention is important, a physician’s suspicion of MRSA involvement should indicate a treatment of vancomycin or linezolid for treatment until testing proves otherwise.