الفهرس 
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Abstract
The aim of this study was directed to make complete bacteriological and immunological studies on some strains of E. coli and Salmonellae known to be highly pathogenic to rabbits in Egypt . The pathogenicity of E. coli 0128: K67 was studied by two methods ; oral infection and ligated intestinal loop . By oral infection ; E. coli caused depression , off food and diarrhoea with 50% mortality . The post mortem lesion showed severe catarrhal enteritis with whitish grey necrotic patches on the mucous membrane of caecum and colon . The toxigenicity of the’o7-ianism was also proved by the ligated intestinal loop . In case of S. tvphimurium , the infected rabbits showed symptoms of illness with yellowish diarrhoea , the mortality rate was 40% and the post mortem examination showed catarrhal gastroenteritis with white necrotic focci in spleen , liver and Peyer’s patches . While in S.enteritidis , the infected rabbits showed more severe symptoms with 60% mortality . Post mortem examination revealed haemorrhagic enteritis , necrotic focci in the internal organs with congestion in the lungs . The immune response of rabbits to these bacterial antigens were also studied. Two types of antigens were prepared from each strain ; formalized and aluminium hydroxide adjuvenated antigens . The antibody titre was measured by TAT and ELISA technique . ELISA technique was very sensitive as it showed reasonable titre even in non-inoculated animals , so TAT had the advantage of direct measuring antibody titre and more practical test for evaluation injected antigen . The antibody titre in rabbits injected with E. coli formalized antigen reached its maximum at 6 weeks from the second dose . In rabbits injected with aluminium hydroxide adjuvenated antigen , the antibody titre was much higher in comparison with the formalized one . This difference remained till the end of the experiment (3 months after second dose) . Antibody titre in rabbits injected with formalized S.tvphimurium antigen showed slight decrease after two weeks from first injection when measured by ELISA technique, while in TAT the antibody titre remained constant at this period . This proved the sensitivity of ELISA technique and gave us attention to inject the second dose at the end of second week instead of the third week . In aluminium hydroxide adjuvenated S. typhimurium antigen , the antibody titre increased continuously till reached the maximum of four weeks post second dose with higher titre than formalized antigen .
The titre increased continuously for three weeks after injection with formalized S. enteritidis antigen . So, the third week is the suitable time for boostering . Balladi rabbits responded well to S. enteritidis antigen more than S. typhimurium antigen . The maximum antibody titre in adjuvenated S. enteritidis antigen was higher by 30 — 35% than the adjuvenated S. typhimurium antigen , this difference was continued the end of the experiment . Adjuvenated aluminium hydroxide antigens showed higher immune response than formalized antigens as the antigen adsorbed onto the aluminium retained at the site of injection and slowly released to the immune system to prolong the immune response .