In vitro activity of fusidic acid against streptococci isolated from skin and soft tissue infections

The in vitro activity of fusidic acid was evaluated against 242 strains of streptococci Isolated from skin and soft tissue infections during a prospective multicentre study. Nearly 90% of strains were isolated from dermatology, emergency and medicine units. Groups A, B, C and G streptococci represented, respectively, 41.9, 20.6, 4.4 and 27.8% of the strains. The activity of fusidic acid was dependent on the media used. MICs were generally one dilution lower with heart infusion agar than with Mueller-Hinton agar supplemented with 5% horse blood (MIC 90 for the whole streptococcal population = 8 mg/L and 16 mg/L, respectively). The distribution of MICs was unimodal and only two strains displayed MICs of fusidic acid ≥ 64 mg/L. In both media, fusidic acid was moderately active against streptococci. However, antibiotic concentrations obtained in the skin exceed the MIC 90 of fusidic acid for streptococci, possibly explaining its clinical efficacy in the treatment of common cutaneous infections.