Abstract: Objectives: Yolk sac infection Escherchia Coil of broiler chickens is major cause during the first week post – hatching. It may cause 100% mortality but the mortality rate is usually between 5% and 10%. On the other hand, a wide range of Extraintestinal pathogenic Escherichia coli (EXPE) occur, which is very important to identify the causative agents and ways to prevent it. Materials & Methods: In this research 600 samples (from 120 farms) were randomly taken from called chicks (1 – 7) days during the one-year period. After DNA extraction, the PCR molecular method was used to evalutev the presence of fimC, tsh, iucD and papC virulence genes. Results & Conclusion: The result showed that 30 sample (5%) from isolated bacteria were E. coli. The frequency of fimC 28 (93/33), tsh 23 (76/66), iucD19 (63/33) and papC 18 (60%) genes was in the isolates. All of the studied genes were present in poultry isolated, as well as from chickens aged one to two days, not isolated from Escherichia coli. According to the identification of fimC, tsh, iucD ana papC genes, it can conclude that these genes can be considered as effective factors in the extraintestinal presence of bacteria. Among them, fimC and tsh genes, due to having the highest prevalence, are likely to cause Escherichia coli pathogens in this region. Fecal contamination of eggs is considered to be the most important source of infection. So, fumigating or disinfection of eggs within 2 hours after they are laid could reduce contamination rate.
