Xunde Li1,2*, Sharif S. Aly2,3, Zhengchang Su4, Richard V. Pereira2, Deniece R. Williams3, Paul Rossitto3, John D. Champagne3, Jennifer Chase1, Tran Nguyen1 and Edward R. Atwill1,2*
The objective of the study was to characterize profiles of phenotypic antimicrobial resistance of enteric bacteria from dairy cattle in different ages and management units. Feces were collected from Holstein and Jersey cattle in different management units on a large Central California dairy including hutch calves (pre-weaned), post-weaned heifers, breeding heifers, springer’s (pregnant nulliparous females due to calve), fresh (recently calved) uniparous (first lactation) cows, fresh multiparous (second or greater lactation) cows, mid-lactation multiparous cows, pregnant late lactation multiparous cows, far-off (recently) dry cows (non-lactating), close up (1-3 week due to calve) dry cows, hospital pen, and mid to late lactation multiparous cows. E. coli and Enterococcus were isolated from fecal samples from cattle in different management units and tested for susceptibility to antimicrobial drugs. E. coli from hutch calves showed a wide spectrum of resistance to antimicrobial drugs compared to isolates from other management units. Enterococcus isolated from all management units was resistant to a wide spectrum of antimicrobial drugs. The drugs that E. coli and Enterococcus were most likely resistant to were tetracycline and lincomycin, respectively. Results of this cross-sectional study showed different antimicrobial resistance profiles of bacteria from dairy cattle of different ages and in different management units. Information can be considered for farm managements to mitigate antimicrobial resistance.