الفهرس 
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Abstract
The present work studies and investigates the poss1b11ity of constructing by the methods of genetic engineering a safe, active and avirulent strains of salmonella typh1 that can be used as a safe active attenuated vaccine for typhoid fever, since typhoid fever considered a major public health proplem in the third world including Egypt in which the disease is endemic and there is a particularly high incidence of the disease in school-age children. The pathogenic strains of selmonella were isolated from patients with typhoid fever for two weaks at least snd the isolated three strains were investigated to assure that it is salmonella strains by biochemical reactions and slide agglutination tests. These three strains on which this work was done. The three strains were subjected to a series of )iochemlca I reactions through the AP I system for enterobacter iaceae and the three strains were give the it cture of salmonella group and these three strains were.