In vitro Antibacterial Activity of the Combination of Florfenicol and Colistin Sulfate on Escherichia coli and Streptococcus Isolated from Pigs

The in vitro antibacterial activities of florfenicol and colistin sulfate against the Escherichia coli and Streptococcus isolates derived from pigs were investigated by checkerboard method in this paper.The results showed that both of the E.coli and Streptococcus isolates were tolerant to florfenicol and the minimum inhibitory concentrations(MIC) were 0.64-5.12 mg/L.Most of the E.coli isolates were resistant to colistin sulfate except one case.When used combined,the fractional inhibitory concentrations(FIC) of florfenicol and colistin sulfate varied from 0.031 26 to 0.140 63,and represented the synergistic effects when the concentration exceed or equal to 0.16 mg/L.