Antimicrobial susceptibilities and genomic characteristics of methicillin-resistant Staphylococcus aureus resistant to mupirocin in Stockholm, Sweden.

The aim of this study was to investigate antimicrobial susceptibilities and genomic characteristics of mupirocin-resistant MRSA isolates in Stockholm, Sweden. In total, 44 non-duplicate mupirocin-resistant MRSA isolates detected in Stockholm during 2010-2022 were investigated. Antimicrobial susceptibility testing was performed using broth microdilution method and further tested for high-level mupirocin-resistance (MuH) and rifampicin by Etest®. All isolates were subjected to whole genome sequencing. 41 isolates presented MuH with MICs ≥1024 mg/L whilst three isolates displayed low-level mupirocin resistance (MuL). mupA-gene was detected in all MuH isolates. Point mutations in ileS gene leading to N213D and V588F were identified in the three MuL isolates. Mutation in rpoB (H481N) was detected in a rifampicin-resistant isolate. Among the isolates, 15 multi-locus sequence types (MLST) were identified, with the four most common sequence types (ST22, ST72, ST8, and ST125) accounting for 66% of the isolates. Mupirocin-resistant MRSA in Stockholm was uncommon, with a percentage of <0.5% among MRSA cases during 2010-2022. In the present study, most mupirocin-resistant isolates were MuH and mupA-positive, predominantly linked to ST22 or ST72 isolates. MuL-resistance was associated with a point mutation in the IleS protein. A multidrug-resistant ST1-MRSA-IV strain was resistant to both mupirocin and rifampicin.