الفهرس 
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Abstract
Avian colibacillosis is an economically important infectious disease of domestic poultry and its etiologic agent is avian pathogenic Escherichia coli (APEC). Among the tools available for the control APEC, vaccines have received the most attention because chemotherapy has met with limited success because of resistance to existing chemotherapeutic agents and the lack of new and effective agents.
This work was planned as an Attempt to evaluate the protective ability of aroA mutant E. coli vaccine against homologues (E. coli O78) and heterologous (E. coli O125) challenge in broiler chickens and prove if that, immunocompetence, is accompanied with rapid vaccine clearance from the vaccinated host or not, with focusing on the immune reactions in response to vaccination with this aroA mutant E. coli vaccine as well compare the bacteriogical identification of the vaccinal strain versus virulent field strains of E. coli, phenotypically and genotypically to stand upon similar virulence characters between them.
For attaining this goal :
Firstly, comparative bacteriological examination was carried between aroA mutant E. coli vaccinal strain and virulent isolated APEC strains (O78 and O125) and demonstrated that the vaccinal and virulent strains were similar in respect of colony morphology, biochemical reactions, Congo Red dye binding and motility but differ in antimicrobial sensitivity pattern as well inability of vaccinal strain to grow on minimal agar medium incontrast virulent strain able to grow. In addition, DNA PCR amplicon of aroA gene was detected in vaccinal strain (deletion mutant) and cannot be detected in field strains due to it is too long and need restriction digestion.