Staphylococcus aureus ST764-SCCmecII high-risk clone in bloodstream infections revealed through national genomic surveillance integrating clinical data.

Summary

National genomic surveillance integrating clinical outcomes identified MRSA ST764-SCCmecII as a high-risk bloodstream clone with the highest 30-day mortality in Japan. Phage-mediated acquisition of superantigen toxins and resistance elements drove its divergence from the New York/Japan clone circa 1994.

Key Findings

• Among 580 bloodstream S. aureus isolates (2019–2020), MRSA ST764-SCCmecII showed the highest 30-day in-hospital mortality.
• ST764-SCCmecII diverged from the ST5-SCCmecII New York/Japan clone, acquiring superantigen toxin phages and resistance genes via mobile elements since around 1994.
• Integrated genomic-clinical surveillance across Japan mapped clonal distribution between eastern and western regions and highlighted three dominant clonal complexes.

Clinical Implications

Hospitals should consider genomic surveillance to detect high-risk MRSA lineages; recognizing ST764-SCCmecII may inform empiric MRSA coverage, isolation policies, and resource allocation.

Limitations

• Observational design limits causal inference; potential sampling bias and generalizability beyond Japan.
• Clinical management implications (e.g., empiric therapy changes) were not prospectively tested.

Future Directions

Implement prospective genomic-informed stewardship to test whether recognizing high-risk MRSA lineages reduces mortality and transmission.