Objectives:Colibacilosis is one of the most important diseases in poultry industry that causes vast economic losses, and it is also dangerous in terms of public health. Antibiotic treatment is the most important tool in dealing with the disease. Antimicrobial susceptibility of isolates must be determined before choosing an antibiotic drug. This study conducted to evaluate sulfonamide resistance phenotype and genotype of E.coli isolates. Material and methods: In this study 44 strains of Escherichia coli were isolated from total of 30 broiler chicken flocks of Urmia city and Its sensitivity to five antibiotics disk, including Enrofloxacin, Sulfadiazine, Florfenicol, Neomycin, Oxytetracycline were assessed. Polymerase chain reactions were used to identify Sul1 genes. Results and conclusion:Antibiogram test results showed that 20 isolates were resistant to sulfadiazine as sulfonamide antibiotics. The Resistance rate for each antibiotic was for Sulfadiazine 45.5%, Enrofloxacin 6.8%, Oxytetracycline 79.5%, Florfenicol 13.7% Neomycin 0%. In this study Sul1 gene were detected in 25 isolates from total 44 isolates of Escherichia coli. The results showed that 5 isolates that have had the Sul1 gene does not show antibiotic resistance in antibiogram test. This could indicate a difference in sensitivity of these two tests or lack of proper conditions for the gene expression in these five isolates. The results showed that the resistance rate of isolates to sulfonamides was high and antibiotic resistance in these two tests, polymerase chain reaction and antibiogram, can be varied.

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