Longitudinal effects of enrofloxacin or tulathromycin use in preweaned calves at high risk of bovine respiratory disease on the shedding of antimicrobial-resistant fecal Escherichia coli

摘要

The objective of this study was to longitudinallyquantify Escherichia coli resistant to ciprofloxacin andceftriaxone in calves treated with enrofloxacin or tulathromycinfor the control of bovine respiratory disease(BRD). Dairy calves 2 to 3 wk of age not presentingclinical signs of pneumonia and at high risk of developingBRD were randomly enrolled in 1 of 3 groups receivingthe following treatments: (1) single label dose ofenrofloxacin (ENR); (2) single label dose of tulathromycin(TUL); or (3) no antimicrobial treatment (control,CTL). Fecal samples were collected immediately beforeadministration of treatment and at d 2, 4, 7, 14, 21, 28,56, and 112 d after beginning treatment. Samples wereused for qualification of E. coli using a selective hydrophobicgrid membrane filter (HGMF) master grid.The ENR group had a significantly higher proportionof E. coli resistant to ciprofloxacin compared with CTLand TUL at time points 2, 4, and 7. At time point 28,a significantly higher proportion of E. coli resistant tociprofloxacin was observed only compared with CTL.The TUL group had a significantly higher proportion ofE. coli resistant to ciprofloxacin compared with CTL attime points 2, 4, and 7. None of the treatment groupsresulted in a significantly higher proportion of E. coliisolates resistant to ceftriaxone. Our study identifiedthat treatment of calves at high risk of developing BRBwith either enrofloxacin or tulathromycin resulted in aconsistently higher proportion of ciprofloxacin-resistantE. coli in fecal samples.