Susceptibility of Skin and Soft-tissue Isolates of Staphylococcus aureus and Streptococcus pyogenes to Topical Antibiotics: Indications of Clonal Spread of Fusidic Acid-resistant Staphylococcus aureus

Abstract

Staphylococcus aureus (SA) isolates (n=255) from outpatients with skin and soft-tissue infections were collected in 3 different areas in Norway. Group A streptococci (GAS, n=68) were isolated from skin or pharyngotonsillar specimens from outpatients. Minimum inhibitory concentrations (MIC) of bacitracin, fusidic acid and mupirocin were tested using the E-test. Pulsed field gel electrophoresis (PFGE) patterns of fusidic acid-sensitive (FusS) and -resistant (FusR) SA were compared. All GAS isolates showed MIC of bacitracin of =1.0 mg/l, of mupirocin of =0.125 mg/l and of fusidic acid 1.0–4.0 mg/l. All the SA showed MIC of mupirocin =0.5 mg/l and of bacitracin of =2.0 mg/l, 91% with MIC=16 mg/l. FusR was shown by 32.5% of the SA strains with similar prevalence rates in 3 different geographical areas of Norway. One particular PFGE pattern (type 1) was shown by 76% of the FusR SA. SA of type 1 belonged to phage group II and produced exfoliative toxins. Thus, the results demonstrated a high prevalence of FusR among SA causing skin infections and that this was mainly due to dissemination of clonally related FusR SA.