Abstract

The aim of this study was to investigate the antimicrobial resistance and to characterize the implicated genes in Escherichia coli isolated from diarrheic calves during 2008-2011. A total of 104 samples were tested to 15 antimicrobial agents with disk-diffusion method.High resistance to amoxicillin, streptomycin, tetracycline, trimethoprim-sulfamethoxazoleand doxycycline was detected. A total of 13 out of the 16 resistance genes were searched in this study. The principal mechanisms of resistance found in the 104 calf isolates wereblaTEM (84.6%), aadA1(73.3%), cmlA(46.2%), tet(B)(79.8%), sulI (74.0%) and dhfrV(54.8%). One kind of amino acid change in gyrA (four Ser83→Leu) and sixteen in parC (twelve 80Ser→Arg, four 80Ser→Ile) were identified in the 20 fluoroquinolone-resistant isolates. According to pulsed field gel electrophoresis (PFGE) results, clonal dissemination of multi-drug resistance (MDR) strains played an important role in the severe resistant situation among diarrheic neonatal calves in northeastern China.

Key words: Escherichia coli, calf, antimicrobial resistance, resistance genes, clonal dissemination