الفهرس 
Clinicopathological studies on avian colibacillosis in broilers
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Abstract
This study aimed to evaluate the most predominant strain of avian pathogenic Escherichia coli (APEC) causing colibacillosis with respiratory manifestation in broiler chickens in Egypt. Isolation and serotyping identification for the isolates of E. coli were performed. Prevalence of APEC was made by detection of the 8 virulence-associated genes 2astA, iss, irp2, papC, iucD, tsh, vat, and cva/cvi3 using multiplex PCR. Antibacterial sensitivity test for antibiotics disc and oregano at different concentrations (20%, 15%, 10%, and 5%), were estimated for the most important isolates of E. coli. After that, evaluating the efficacy of oregano oil 20% (in drinking water) and oregano powder 10% (on diet) for treatment and prophylaxis of broiler chickens experimentally infected with APEC O27-local isolate was performed. A total of 300 chicks -aged 19 days oldwere randomly allocated into equal 6 groups; normal control (G1), Infected (G2), oregano treated (G3), antibiotic treated (G4), oregano control (G5), and oregano treated then infected (G6). Chickens of (G5) and (G6) were supplemented with oregano powder that contains 10% oregano essential oil in the diet (250 g /ton diet) from the 1st day old till the end of the experiment. At the age of the 19th, 20th, and 21st day, G2, G3, G4, and G6 were infected with 0.2ml of APECO27 (1{u00D7}107 CFU/chick) via the intratracheal route. On the 22nd, 23rd, and 24th day of age, chicks of G3 & G4 were treated with oregano 20% (2 ml per 5 liters) and difloxacin (10 mg/kg b.wt.) in drinking water, respectively. On the 3rd, 6th, 10th, and 21st day post-infection, blood and tissue samples were collected from all groups for laboratory examination of the hemogramserum biochemistry, and histopathology of the vital organs. Results revealed that E. coli O27 was the most predominant serotype strain (11 out of 35 isolates)