Thesis (Ph.D.) - Cairo University - Faculty of Veterinary Medicine - Department of Microbiology

150 samples examined from different sources of chicken(Broiler, Breeder, chicks, and environmental samples), the results revealed that the percentage of isolation of E.coli was 66.7%. The results of the serological identification of 100 isolates of E. coli from cases showing symptoms of colisepticemia revealed that the isolates could be typed under different serotypes. 100 isolates were distributed as 19 (19%) of serotype untypable, 17 (17%) of serotype O125:K70, 14 (14%) of serotype O91:K, 11 (11%) of Rough strain, 8 (8%) of serotype O153, O78:K80 and O145:K- each, 6 (6%) of serotype O158:K- and O1:K26 and 3 (3%) of serotype O115. In this study, all isolates of E. coli strains were sensitive to cephradine and fosfomycine in apercentage of 100% while Ampicillin, Amoxaicillin, spectinomycine and Erythromycine were 100% resistance. Virulence assays revealed that E.coli isolates were positive in Motility test, Haemolytic activity, Congo red binding assay and serum resistance in a percentage of 100%, 90%, 83%, and 62% respectively. In Embryo lethality assay, result revealed that O78K80 was 80% pathogenic while O1 K26 was 10% pathogenic. In this study, all E.coli serovars were positive for 16SRNA in apercentage of 100%. The result of multiplex PCR for virulence genes ( ompA, iss, fimH) revealed that E.coli serovars were positive in a percentage of 100%, 92%, and 77% respectively

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