Emergence of Daptomycin-Nonsusceptible Methicillin-Resistant <italic>Staphylococcus aureus</italic> Clinical Isolates Among Daptomycin-Naive Patients in Korea.

This study was conducted to assess emergence of daptomycin-nonsusceptible (DAP-NS) phenotype in DAP-naive patients with invasive <italic>Staphylococcus aureus</italic> (ISA) infections in Korea. A total of 208 <italic>S. aureus</italic> clinical isolates were selected from a previous prospective study on ISA infections and evaluated for DAP-NS. Although DAP has never been introduced in Korea, five DAP-NS <italic>S. aureus</italic> strains (2.4%) were identified among 208 <italic>S. aureus</italic> strains collected from ISA infections. The DAP-NS phenotype was observed only in methicillin-resistant <italic>S. aureus</italic> (MRSA) strains, but not in methicillin-susceptible <italic>S. aureus</italic> strains. One DAP-NS MRSA strain belonged to sequence type 72 (ST72) and four were ST5 MRSA strains, three of which were heteroresistant vancomycin (VAN)-intermediate <italic>S. aureus</italic>. All these five DAP-NS MRSA strains were from healthcare-associated infections without prior exposure to VAN within 30 days. While the ST72 MRSA strain exhibited DAP-NS phenotype via charge repulsion mechanism, four ST5 DAP-NS <italic>S. aureus</italic> strains had charge-independent DAP-NS mechanism. None of the five DAP-NS strains displayed significant increase in cell wall thickness, indicating that altered cell wall thickness was not associated with the observed DAP-NS phenotype. [ABSTRACT FROM AUTHOR]