Abstract
The in vitro susceptibilities of 50 field isolates of Riemerella anatipestifer from ducks to ceftiofur and 16 other commonly used antimicrobials were determined. The MIC90 values (MIC refers to minimum inhibitory concentrations) for the antimicrobials used in this study are as follows: penicillin was 16 μg/ml; ceftiofur was 32 μg/ml; cephalothin, chloramphenicol, flumequine, and kanamycin were 64 μg/ml; nalidixic acid, nitrofurantoin, and sulfamethoxazole were 128 μg/ml; amikacin, ampicillin, gentamicin, lincomycin, spec-tinomycin, streptomycin, tetracycline, and trimethoprim were ≥256 μg/ml. The therapeutic efficacy of ceftiofur against a highly lethal experimental R. anatipestifer infection in ducks was also evaluated. All experimental ducks were infected through the infraorbital sinus with 1 ml of 9 × 109 CFU of R. anatipestifer. Ceftiofur (0, 0.25, 0.5, 1, and 2 mg/kg) was injected subcutaneously 5 hours after infection. A single dose of 2 mg/kg resulted in 73% survival as compared with 10% survival in the infected, but untreated controls.