Oxacillin- and Mupirocin-Resistant Staphylococcus aureus: In vitro Activity of Silver Sulphadiazine and Cerium Nitrate in Hospital Strains

Abstract

Nasal carriage is an important reservoir of oxacillin-resistant Staphylococcus aureus (ORSA). Mupirocin is a topical drug used to remove S. aureus from nares. However, isolates resistant to mupirocin have been reported all over the world. Silver sulphadiazine (SSD) is a topical agent, which when associated with cerium nitrate (CN), has been shown to be useful in the treatment of burn infections and could be an alternative drug for patient decolonization. Susceptibility to oxacillin in 203 S. aureus isolates was evaluated by the agar diffusion test, while the agar diffusion and agar dilution methods were used for mupirocin. A PCR-multiplex method was performed to detect the mecA and ileS-2 genes. Minimum inhibitory concentration (MICs) to SSD and CN, used alone or in association, were determined by the agar dilution method. One hundred and sixty-three (80.3%) strains were oxacillinresistant, and 37 (18.2%) were mupirocin resistant. The MIC of SSD alone or in association with CN was 64 μg/mL, while for CN alone was 2,048 μg/mL for all isolates. SSD presented anti-staphylococcal activity at concentrations (64 μg/mL) much lower than those commonly used in commercial preparations (10 mg/g) and had good activity against mupirocin-resistant strains, showing that this drug could be used for nasal decolonization in ORSA carries.

Keywords:

• Staphylococcus aureus
• oxacillin resistance
• mupirocin resistance
• silver sulphadiazine and cerium nitrate