Acquisition of high-level mupirocin resistance and its fitness cost among methicillin-resistant Staphylococcus aureus strains with low-level mupirocin resistance.

We investigated whether methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) isolates with low-level mupirocin resistance can serve as recipients of a pSK41-like plasmid conferring high-level mupirocin resistance without substantial fitness cost. Our results suggest that acquisition of the plasmid conferring high-level mupirocin resistance was not necessarily associated with fitness cost in some MRSA recipients with low-level mupirocin resistance.