Decrease in the incidence of mupirocin resistance among methicillin-resistant Staphylococcus aureus in carriers from an intensive care unit

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a serious nosocomial problem, globally distributed. Decolonization with mupirocin can be used to control its dissemination. Objective: To determine the incidence of mupirocin resistance among MRSA carriers from an intensive care unit. Methods: We obtained 2723 nasal swabs during 3 years. Resistance to methicillin and mupirocin were verified (agar diffusion and the E test) and confirmed by polymerase chain reaction (PCR) (mecA for methicillin; ReS-2 and mupA for mupirocin). Plasmid-curing procedure and pulsed-held gel electrophoresis (PFGE) were employed in isolates exhibiting high resistance to mupirocin (HR-Mup) and in other selected organisms. Results: The overall incidence of HR-Mup among MRSA carriers during the studied period was 4.84% (8/165); however, the incidence decreased from 13.04% (6/46) in the first year to 3.5% (2/57) in the second year and was 0% in the last year (P = .02). LR-Mup, in contrast, increased significantly (P = .01). Conclusion: Plasmid-curing procedure showed the plasmid location of genes responsible for HR-Mup. PFGE demonstrated that most MRSA, including the isolates with HR-Mup, were genetically related, The decline in HR-Mup may be attributable to the plasmid location of genes (ileS-2/mupA) and to the fact that all patients colonized with HR-Mup MRSA died or were discharged in a relatively short period of time.