A detoxified recombinant E. coli heat-labile enterotoxin mutant, LTS61K, is employed as a carrier protein to conjugate polysaccharide. The LTS61K contains a mutated mature sub-unit A (LTA) that includes lysine at amino acid position 61 and a wild-type mature sub-unit B (LTB). Various types of bacterial capsular polysaccharide antigens were chemically conjugated with the LTS61K protein by a reductive amination reaction. The conjugated polysaccharide-LTS61K products were physically, chemically and biochemically identified as soluble form. Rabbits were immunized intramuscularly to determine the immunogenicity of conjugated vaccines by ELISA to detect anti-polysaccharide antigen IgG titers and serum bactericidal assay thereby determining the functional activity of the antibodies. Study results show that conjugated polysaccharide-LTS61K vaccines induce higher polysaccharide-specific IgG titers and greater bactericidal activity in sera than that of polysaccharide alone or polysaccharide mixed with LTS61K. The presence of anti-LTS61K serum IgG antibody alleviates travel diarrhea caused by E. coli (ETEC enterotoxigenic E. coli).
