Abstract: [Objective] To determine the pathogenic bacteria causing calf diarrhea in a cattle farm in Duolun County, Xilin Gol League, Inner Mongolia, and to provide a basis for selecting sensitive drugs to treat this disease. [Method] Anal swabs from calves with diarrhea were collected aseptically for bacterial isolation, identification, pathogenicity test and in vitro antimicrobial sensitivity test. [Result] The bacterial strains isolated from the anal swab samples had the consistent colony morphology. The isolates were confirmed as Escherichia coli （E. coli） by phenotypic identification, physiological and biochemical identification and 16S rDNA gene sequencing identification. The isolates were molecularly identified as ETEC type by using the E. coli typing primers. In addition, the E. coli isolates could cause mice death. The E. coli isolats were resistant to 21 antimicrobial agents such as ampicillin, aztreonam, cefazolin, tetracycline, ofloxacin, levofloxacin and compound trimethoprim, were moderately sensitive to 10 antimicrobial agents such as cefoperazone, ceftriaxone, clindamycin, polymyxin B and minocycline, and were sensitive to 4 antimicrobial agents such as cefoxitin, vancomycin, ciprofloxacin and nitrofurantoin. [Conclusion] The calf diarrhea in this cattle farm was caused by enterotoxigenic E. coli. Ciprofloxacin was recommended to be used in treatment of this disease.

Key words: Escherichia coli, calf, diarrhea, isolation and identification