Brazilian methicillin-resistant Staphylococcus aureus (MRSA) strains carrying a diversity of mupirocin-resistance plasmids

Methicillin-resistant Staphylococcus aureus (MRSA) are widespread causative agents of hard-to-treat infections in the nosocomial environment, with increasingly narrower treatment possibilities. Mupirocin is an antibiotic commonly used to promote nasal decolonization and prevent transmission of MRSA in hospitals. Resistance to high levels of mupirocin is emerging globally, being mainly conferred by the product of the mupA gene. In this study, we analyzed the levels of resistance to mupirocin, the presence of the mupA gene, the transmissibility and diversity of plasmids among Staphylococcus isolated from nosocomial infections. Five mupA -carrying and mupirocin-resistant MRSA strains were studied in terms of the plasmidial origin of mupA , which was confirmed by curing during heat stress, plasmid extraction and PCR. Resistance was associated with high-molecular weight plasmids, which were transferred by conjugation to methicillin-sensitive S. aureus , and then to a MRSA strain. The plasmids were shown to be diverse by analysis of the presence, orientation, and distance of the insertion sequence IS 257 from the mupA gene, and by their restriction patterns. This study reinforces that, given the decline of possibilities to treat MRSA infections and the easy transfer of mupirocin-resistance plasmids among Staphylococcus , the use of this antibiotic must be carefully monitored.