Resistance patterns and detection of resistance genes in Escherichia coli isolated from diarrheic calves in Northeastern China

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