In-vitro antibacterial activity of fusidic acid alone and in combination with other antibiotics against methicillin-sensitive and -resistant Staphylococcus aureus.

The activity of fusidic acid alone and in combination with gentamicin, oxacillin, rifampicin, fosfomycin and ciprofloxacin was investigated against 36 strains of Staphylococcus aureus. The fusidic acid MIC50 of 0.06 mg/L and MIC90 of 0.125 mg/L were determined for 36 strains. Bactericidal activity of fusidic acid was confirmed. Several types of interaction were observed with other antibiotics: dominant effect of fusidic acid over gentamicin; synergy with rifampicin for three or four strains; indifference or dominance with oxacillin, indifference with vancomycin, indifference or dominance with fosfomycin, and indifference with ciprofloxacin. Antagonism was seen with only one strain, following exposure to fusidic acid and rifampicin.