Cell wall structures which may be important for successful immunization with Salmonella-Shigella hybrid vaccines.

Three separate lots of S. typhi/S. sonnei hybrid (Ty/Shig) live oral vaccine strain 5076-1C were tested for efficacy in human volunteers challenged with virulent S. sonnei. Two lots (2 and 5) protected volunteers, a third lot (8) did not. The three lots were evaluated by immunological tests and electron microscopy. Lots 2 and 5, which protected, contained bacteria that reacted with anti-flagellar serum and had observable attached flagella and pili. Lot 8, which failed to protect, did not react with anti-flagellar serum, and had no observable pili. There was no correlation between vaccine efficacy and the reaction of IgG in patient's sera in western blot analysis. Surface structures on the Ty-Shig hybrid may be important for generating a protective immune response.