Abstract: This study aimed to determine the pathogenic bacteria causing the calf diarrhea in a beef cattle farm in northwestern Hunan Province, and to characterize their antimicrobial resistance profile. The pathogenic bacterial strains were isolated and identified by using routine culture method, Gram's stain method, microscopic examination and biochemical reaction tests. Antimicrobial susceptibility test of the isolates was performed by Kirby-Bauer disk diffusion method. The results showed that the dominant causative agents associated with the calf diarrhea in this beef cattle farm were identified as Escherichia coli(E. coli); the E. coli clinical isolates were sensitive to cefoperazone, cefazolin, minocycline and ceftriaxone, moderately sensitive to cefuroxime and ceftazidime, and resistant to 22 kinds of antimicrobial agents, including cephalexin, piperacillin, erythromycin, vancomycin, doxycycline, etc. The isolated E. coli strains exhibited resistance to various antibacterial drugs, and our results provided an effective basis for scientific diagnosis and treatment of calf diarrhea.

Key words: calf, diarrhea, Escherichia coli, isolation and identification, antimicrobial resistance analysis