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 prospec tive multicentre study. Nearly 90% of strains were isolated from dermatolog y, emergency and medicine units. Groups A, B, C and G streptococci represen ted, respectively, 41.9, 20.6, 4.4 and 27.8% of the strains. The activity o f fusidic acid was dependent on the media used. MICs were generally one dil ution lower with heart infusion agar than with Mueller-Hinton agar suppleme nted with 5% horse blood (MIC90 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, greater than or equal to 6 4 mg/L. In both media, fusidic acid was moderately active against streptoco cci. However, antibiotic concentrations obtained in the skin exceed the MIC 90 of fusidic acid for streptococci, possibly explaining its clinical effic acy in the treatment of common cutaneous infections.