A retrospective study of 132 cases of natural Escherichia coli infection in preweaning piglets with diarrhea submitted to the Department of Veterinary Pathology in Seoul National University from 1995 to 1996 was performed to determine the biochemical characteristics and antibiotics susceptibility. Most field isolates were lysine decarboxylase-positive (99.2%), phenylalanine decarboxylase-negative (100%), and fermented sorbitol (91.7%). Antibiotic susceptibilities will be determined by agar diffusion method. A large percentage of isolates were resistant to many antibiotics in common usage. Most isolates were susceptible to colistin (98.8%), gentamycin (64.3%), amikacin (100%), and ceftiour sodium (64.2%), whereas most isolates were notably resistant to ampicillin (86.9%), neomycin (66.7%), streptomycin (84.5%), tetracycline (98.8%), penicillin (98.8%), and amoxacillin (58.3%).
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