In vitro activity of two old antibiotics against clinical isolates of methicillin-resistant Staphylococcus aureus

The objective of this paper was to investigate the in vitro effects of fusidic acid combined with fosfomycin against methicillin-resistant Staphylococcus aureus (MRSA). In all, 196 MRSA strains isolated from three clinical specimens of human infections from hospitals in China were used in this study. The checkerboard method was used to determine whether combinations act synergistically against these strains. The susceptibility results for fusidic acid and fosfomycin were interpreted according to the guidelines of the Clinical and Laboratory Standards Institute. The combination of fusidic acid and fosfomycin demonstrated the following interactions: 87.76% (172/196) synergism, 12.24% (24/196) indifference and no antagonism was seen (minimum and maximum fractional inhibitory concentration index 0.14 and 0.75, respectively). Thus, combinations of fusidic acid and fosfomycin show synergism for most of the MRSA isolates tested in this study, and may be a future therapeutic alternative for infections caused by MRSA. The Journal of Antibiotics (2010) 63, 657-659; doi:10.1038/ja.2010.105; published online 29 September 2010