Genetic nature and virulence of community-associated methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) emerged in 1961, just after the introduction of methicillin as a countermeasure against penicillinase-producing “multidrug-resistant” S. aureus, a threat at that time. Since then, MRSA has posed a continuous threat to medical care as a major multidrug-resistant pathogen in hospitals. In 1997-1999, severe invasive infection with MRSA occurred in the community, and this attracted attention as community-associated MRSA (CA-MRSA). The evolutionary steps include species-to-species transfer and salvage of key genetic structures, responsible for community spread, virulence, and resistance. The MRSA epidemic, including invasive diseases, in the community is dynamic.