Molecular Epidemiological Features of Methicillin-Resistant Staphylococcus aureus in Japan

Recently, the epidemic types of methicillin-resistant Staphylococcus aureus (MRSA) in hospital and community settings in Japan have changed significantly. Before 2010, approximately 80% of the MRSA strains isolated from hospitals were typical healthcare-associated MRSA (HA-MRSA) with staphylococcal cassette chromosome (SCC) mec type II. However, USA400-like community-associated MRSA (CA-MRSA) with SCCmec type IV (defined as USA400/J) has become dominant in hospitals since 2014. By contrast, skin infections caused by the highly virulent CA-MRSA USA300 clone have increased. The USA300 clone is associated with intractable skin infections and necrotizing pneumonia because it carries a cytolytic pore-forming toxin, Panton-Valentine leukocidin (PVL), and an arginine catabolic mobile element that promotes skin colonization. In the past decade, the USA300 clone has shown limited prevalence and has not been considered a serious problem in Japan. However, the USA300 clone has recently spread in community and hospital settings. This review discusses the evolution and current status of the molecular epidemiological features of HA-MRSA and CA-MRSA strains in Japan.