COMPARISON OF MICS OF CEFTIOFUR AND OTHER ANTIMICROBIAL AGENTS AGAINST BACTERIAL PATHOGENS OF SWINE FROM THE UNITED-STATES, CANADA AND DENMARK

The MICs of ceftiofur and other antimicrobial agents, tested for compa rison, for 515 bacterial isolates of pigs from the United States, Cana da, and Denmark with various diseases were compared. The organisms tes ted included Actinobacillus pleuropneumoniae, Escherichia coli, Pasteu rella multocida, Salmonella choleraesuis, Salmonella typhimurium, Stre ptococcus suis, Streptococcus dysgalactiae subsp. equisimilis, Strepto coccus equi subsp. equi, and Streptococcus equi subsp. zooepidemicus. In addition to ceftiofur, the following antimicrobial agents or combin ations were tested: enroflaxacin, ampicillin, sulfamethazine, trimetho prim-sulfadiazine (1:19), erythromycin, lincomycin, spectinomycin, lin comycin-spectinomycin (1:8), tilmicosin, and tetracycline. Tilmicosin was only tested against the U.S. isolates. Overall, ceftiofur and enro floxacin were the most active antimicrobial agents tested against all isolates, with MICs inhibiting 90% of isolates tested (MIC(90)s) of le ss than or equal to 2.0 and less than or equal to 1.0 mu g/ml, respect ively. Erythromycin, sulfamethazine, spectinomycin, and lincomycin dem onstrated limited activity against all of the organisms tested, with M IC(90)s of greater than or equal to 8.0, greater than or equal to 256. 0, greater than or equal to 32.0, and greater than or equal to 16.0 mu g/ml, respectively. Trimethoprim-sulfadiazine was active against isol ates of A. pleuropneumoniae, S. choleraesuis, S. typhimurium, P. multo cida, S. equi, and S. suis (MIC(90)s, less than or equal to 0.5 mu g/m l) but was less active against the E. coli strains tested (MIG(90), >1 6.0 mu g/ml). Ampicillin was active against the P. multocida, S. suis, and S. equi isolates tested (MIC(90)s, 0.5, 0.06, and 0.06 mu g/ml, r espectively) and was moderately active against S. typhimurium (MIC(90) s, 2.0 mu g/ml). However, this antimicrobial agent was much less activ e when it was tested against A. pleuropneumoniae, S. cholerae-suis, an d E. coli (MIC(90)s, 16.0, >32.0, and >32.0 mu g/ml, respectively). Ag ainst the U.S. isolates of A. pleuropneumoniae and P. multocida, tilmi cosin was moderately active (MIC(90)s, 4.0 and 8.0 mu g/ml, respective ly). However, this compound was not active against the remaining U.S. isolates (MIC(90)s, >64.0 mu g/ml), Differences in the MICs from one c ountry to another were not detected with enrofloxacin, ceftiofur, or l incomycin for the strains tested, but variations in the MICs of the re maining antimicrobial agents were observed.