Abstract: 32 strains of Escherichia coli (E. coli) were isolated from 50 E. coli infected chickens in six farms in Shandong. As a result, all of them were resistant to 12 antibiotics to a greater or less degree. In the screening test of plasmid DNA of 14 strains E.coli isolates and plasmid DNA fragments generated by Hind Ⅲ, simple agarosegel electrophoresis was employed. The results showed that most of E.coli isolated from the same infected flocks on the same farm had similar plasmid profile, and its fragments sizes were similar too, and that these isolated had common plasmids. The results showed that those isolates from different chicken flocks and had different plasmids were in different serotypes, the plasmids could be transferred in different serotypes of E.coli.

Key words: chick; E.coli;  antibiotic resistance; biologic identity