الفهرس 
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Abstract
E. coli infections in avian species have become an economic threat to the poultry industry worldwide.
In this study, a total of 200 liver samples were collected from different broiler flocks at different localities in SohagProvince. Over all isolation incidence was 106 suspected E. coli isolates with a percentage 53%.
Thirty five isolates were subjected for isolation and the results were: 13 typeable E.coli isolates (37.1%) and 22 untypeable E.coli isolates (62.8%). Serogroup O78 was the most frequently observed (38.5%) among the typeable isolates.
The objective of this study also, is to determine whether the immunization using commercially available living Escherichia coli vaccines as Nisseiken Avian Colibacillosis Vaccine (Nisseiken Co., Ltd., Ome, Tokyo, Japan) and O78 aroA deleted vaccine (Poulvac ® E.coli, Zoetis) are protective against APEC challenges or not.
Ninety eight chicks (Arbor, Acres) of both sexes were divided into seven groups (14 birds/each); two groups were vaccinated at day 1 of age by spray route using Nisseiken Avian colibacillosis Vaccine, then one of them challenged intratracheally with homologous E.coli O78 and the other with heterologus O1 at day 14, the other two groups were vaccinated at day 1 of age by eye DROP route using Poulvac ® E.coli, Zoetis vaccine then one of them challenged intratracheally with homologus E.coli O78 and the other with heterologus O1 at day 14. The other two groups were positive control (challenged, unvaccinated); one challenged with O78 and the other with O1 at day 14 using intratracheal route. The last group served as environmental control (non vaccinated, non challenged).
At day 28, birds were necropised and examined to evaluate the efficacy of both of the two different vaccines. The best obtained results were recorded to the vaccinated challenged groups with the homologous and heterologous strains and vaccinated by spraying and eye DROP methods which showed a decrease in organ lesion scores in comparison to the other groups (non-vaccinated, challenged broilers). Regarding to weight gain, the vaccinated and negative control groups showed better outcomes than unvaccinated ones.
These results suggest that the two different vaccines used in our study are efficient in reducing lesion scores against homologous and heterologous challenge using spray and eye DROP methods that could lead to minimizing the time for treatment and cases of condemnation in processing plants.
In conclusion, Serotying performed on E. coli isolates duringbthis study suggests that serotype O78 and untypeable isolates were most frequently involved in APEC infections in the investigated broiler flocks.
Regarding to vaccines, Nisseiken Avian Colibacillosis vaccine (Nisseiken Co., Ltd. Ome, Tokyo, Japan) and Poulvac® E.coli, Zoetis vaccine are considered safe to be used in poultry industry and had no undesired effect. Based on the results of this study, they showed an successful role in minimizing the severity of the lesions and clinical signs in vaccinated birds than those unvaccinated ones and consequently they may lead to decrease the economic losses spent every year in the farm.