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.

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 < or = 1.0 mg/l, of mupirocin of < or = 0.125 mg/l and of fusidic acid 1.0-4.0 mg/l. All the SA showed MIC of mupirocin < or = 0.5 mg/l and of bacitracin of > or = 2.0 mg/l, 91% with MIC > or = 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.