الفهرس 
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Abstract
A total of (192) rectal swab was collected from newly weaned dirrhiec rabbits at different seasonal period extended from (April 2014 –March 2015) to examine the presence of E.coli. These isolates were further characterized by biochemical tests and polymerase chain reaction. E.coli was isolated in 84 of the 192 samples (43.75%).Seasonal prevalence of Escherichia coli infection revealed that the highest incidence occurred in summer season 29/44 (65.9%). Followed by spring 21/52(40.4%), then in autumn 19/50 (38%), and finally in winter 15/46 (32.6%).The isolated E.coli strain were found to belong to O stereotypes in order of frequency O158, O128, O125, O27, O18, O20, O148 and Untypable (20%, 13.33%, 13.33 13.33%, 6.67%, 6.67%, 6.67%, and 20% ) isolates respectively). Antibiotic sensitivity testing revealed that the isolated E. coli strains showed high susceptibility rate to Colistine and Gentamycine (100%), Enrofloxacine and Norfloxacine (93.33%), Ampicilline (86.88), followed by Streptomycine (80%), while they were intermediately sensitive to Florofenicole and Neomycine,while they were resistant to some antimicrobial agents, mainly Oxytetracycline ,Chloramphenicol and sulphamethoxazole. Based on PCR, All examined E.coli were positive100 %( 7/7) for eae virulence gene, while 87.8 %( 6/7) of the tested E.coli isolates were positive to tsh gene. It was concluded that Combination of genotypic with phenotypic analysis of E.coli isolates is morevaluable as an epidemiological tool for differentiation and identification of the isolates than one test alone.