الفهرس 
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Abstract
The study of E.coli incidence in 800 chickens and 550 ducks revealed an infection rates of (43.1%) and (27.2%) respectively. The 345 E.coli isolates recovered from chickens were typed in 24 O groups with predominance of the O groups O44, O158, O114, O91, O111, O125, O103, O142, O26, O78, O127 and O164. Of the 15 O groups recovered from ducks, the O158, O103, O125, O44, O114, O91, O111 and O78 were the most predominant. The testing of E.coli isolates for phenotypic and genotypic virulence markers revealed that Congo red binding was positive in (82.6%) and (74.7%) in chickens and ducks isolates, respectively. Corresponding positive rates were (87.5 %) and (76%) for haemagglutination and (73%) and (56.7%) haemolytic activity . Only O44 and O158 recovered from chickens were cytotoxic to vero cells and all O groups isolated from ducks were negative. Most isolates showed multiple-antibiotic resistance.Stx1 gene was detected in one isolate belonging to O158 and Stx2 gene was found also in one isolate of the O group 44.In chicken’s isolates eaeA gene (intimin), was detected in E.coli isolates belonging to the O groups O44, O158, O125, O114 and O78. Iut A gene was detected in E.coli isolates belonging to the O groups O114, O44, O111, O26, O142, O78, O103 and O91. ISS gene was detected in E.coli isolates belonging to the O groups O44, O91, O111, O158, O125, O114, O142, O127, O103, O164 and O119. All of the tested 9 serogroups from ducks were negative for the Stx1 gene, and Stx2 gene eaeA gene (intimin) was detected in E.coli isolates belonging to the O groups O158, O78 and O26. Iut A gene was detected in E.coli isolates belonging to the O groups O114, O44, O91, O111, O26, O158, O78, O103 and O125. ISS gene was detected in E.coli isolates belonging to the O groups O114, O44, O91, O111, O158, O125, O103 and O26.
Three bands of plasmids were detected in four O groups (O44, O158, O111, O114), two bands in O groups (O78, O103 and O125), while only one band was seen in group (O142) recovered from chickens. Three bands of plasmids were detected in two O groups (O158 and O114); two bands in one O group O44 of isolated from ducks. Intratracheal inoculations of one day old chicks of different isolates of E.coli were carried out to detect their pathogencity. The results indicated that serogroups (O44, O158, O114, O111, O91 and O78) caused a mortality rate that varied between (60%-80%), while in serogroups (O103, O125, O142, O26, O127, O164 and O119), the mortality rates were much lower (30%-40%).