In vitro activity of flumequine in comparison with several other antimicrobial agents against five pathogens isolated in calves in the Netherlands

The in vitro activity of flumequine in comparison with several other drugs was tested against 17 P. multocida, 16 P. haemolytica, 21 S. dublin, 21 S. typhimurium and 21 E. coli strains, isolated in (veal) calves in the Netherlands. The MIC 50 of flumequine for the respective pasteurellas was 0.25 and 1 μg/ml, for the salmonellas and E. coli 0.5 μg/ml. In comparison with flumequine, enrofloxacin and ciprofloxacin showed higher in vitro activity, with MIC 50 ≤ 0.008 μg/ml for ciprofloxacin. Decreased susceptibility of the pasteurellas was found for kanamycin, neomycin, streptomycin, gentamicin, oxytetracycline and doxycycline. The MIC 50 of minocycline for P. multocida was 0.5 μg/ml and there was no cross resistance with the other tetracyclines. P. multocida was very susceptible to ampicillin (MIC 50 ≤ 0.03 Ag/ml), P. haemolytica, however, was 100% resistant to this drug. Both pasteurellas were susceptible to cephalothin and approximately 50% of the strains of both bacteria were resistant to chloramphenicol. The MIC 50 of either spiramycin or tylosin was ≥ their respective breakpoint-MIC values. Both pasteurellas were susceptible to the combination of trimethoprim and sulphamethoxazole. However, for P. multocida, the addition of sulphamethoxazole to trimethoprim had no synergistic effect on its MIC. In comparison with trimethorpim, aditoprim was less potent. Therefore only P. multocida was susceptible to aditoprim.