Synergistic antibacterial effects of the combination of sulfamethazine and tiamulin against Salmonella Typhymurium and Actinobacillus pleuropneumoniae isolated from pigs

This study was investigated the synergistic antibacterial effects from the combination of sulfamethazine (SMZ) and tiamulin (SMT) against Salmonella Typhimurium (S. Typhimurium) and Actinobacillus pleuropneumoniae (A. pleuropneumoniae) isolated from pigs. Minimum inhibitory concentrations (MICs) and fractional inhibitory concentration (FIC) index were determined for 10 bacteria from 13 swine farms in Gyeongsangnam province by the National Committee for Clinical Laboratory Standards broth microdilution procedure. Antimicrobial agents tested included SMZ, tiamulin and SMT. Against S. Typhimurium and A. pleuropneumoniae, the MIC ranges of SMZ, tiamulin and SMT were 125-500, 15.625-62.5 and 15.625-62.5 μg/mL, respectively. In addition, the FIC index ranges of SMT against S. Typhimurium and A. pleuropneumoniae were 0.19-0.38 and 0.19-0.62, respectively. In conclusion, SMT has a high antibacterial activity against S. Typhimurium and A. pleuropneumoniae, then the combination may be applied for the treatment of swine diseases caused by S. Typhimurium and A. pleuropneumoniae.