Abstract: To study the resistance transfer mechanism of E.coli in animal farms and the possibility of resistant clones vertical spread between animals and huamns, 86 multidrug-resistant E.coli isolates with similar resistance profiles were characterized by pulsed-field gel electrophoresis(PFGE) after XbaI digestion and drug susceptibility testing to investigate the epidemiologic relationship among the isolates from animals, environment and farmers. The results showed that twenty different PFGE types were found among 37 strains isolated from poultry farm and twenty-four were found among 49 strains isolated from swine farm. The PFGE patterns of strains isolated from the same animal or farmer or environment were often identical. Some E. coli isolates from different animals in the same farm have identical PFGE patterns and some isolates from animals or farmers were identical to some isolates from environments. The PFGE patterns of five E.coli strains, one from chicken, three from one farmer and one from environment were quite heterogeneous. Three E.coli isolates from pig, farmer and environment separately were also found belong to the same PFGE genetype. All isolates were resistant to ciprofloxacin, ampicillin, streptomycin, tetracycline, doxycycline and trimethoprim-sulfamethoxazole. Resistance patterns of isolates with identical PFGE genetype may different. And the same resistance profile may shared by isolates with different PFGE genetype. It is concluded that vertical transmission of resistant E. coli clones between farm animals, environment and farmers were commonly occurs. Resistance spectra and PFGE genetypes were not always uniform.

Key words: E.coli, Multidrug-resistant, PFGE genetype, Animals, Clonal spread