Molecular nature of methicillin-resistant Staphylococcus aureus derived from explosive nosocomial outbreaks of the 1980s in Japan.

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) with Panton-Valentine leukocidin (PVL) genes is increasing worldwide. Nosocomial outbreak-derived (hospital-acquired) MRSA (HA-MRSA) in Japan in the 1980s was also largely PVL+. PVL+ HA-MRSA and CA-MRSA shared the same multi-locus sequence type (ST30) and methicillin resistance cassette (SCCmecIV), but were divergent in oxacillin resistance, spa typing, PFGE analysis or clfA gene analysis. PVL+ HA-MRSA, which probably originated in PVL+ S. aureus ST30, was highly adhesive (carrying cna and bbp genes), highly-toxic (carrying lukPV and sea genes) and highly drug-resistant. PVL+ HA-MRSA was once replaced by other PVL− HA-MRSA (e.g., ST5), and is re-emerging as CA-MRSA.