st8:usa300 st8:usa300 st8:usa300 is a strain of community-associated methicillin-resistant staphylococcus aureus (mrsa) that has emerged as a particularly antibiotic resistant epidemic that is responsible for rapidly progressive, fatal diseases including necrotizing pneumonia, severe sepsis and necrotizing fasciitis. the epidemiology of infections caused by mrsa is rapidly changing: in the past 10 years, infections caused by this organism have emerged in the community (whereas previously mrsa infections were almost exclusively hospital-acquired). the 2 mrsa clones in the united states most closely associated with community outbreaks, usa400 (mw2 strain, st1 lineage) and usa300, often contain panton-valentine leukocidin (pvl) genes and, more frequently, have been associated with skin and soft tissue infections. outbreaks of community-associated (ca)-mrsa infections have been reported in correctional facilities, among athletic teams, among military recruits, in newborn nurseries, and among sexually active men who have sex with men, ca-mrsa infections now appear to be endemic in many urban regions and cause most mrsa infections. methicillin-resistant staphylococcus aureus electron micrograph of mrsa scientific classification domain: bacteria phylum: bacillota class: bacilli order: bacillales family: staphylococcaceae genus: staphylococcus species: s. aureus binomial name staphylococcus aureusrosenbach 1884 type strain "st8:usa300"