LPS-based conjugate vaccines composed of saccharide antigens of smooth-type Salmonella enteritidis and rough-type S. gallinarum 9R bound to bovine serum albumin

Lipopolysaccahrides (LPSs) from Salmonella enteritidis, S. gallinarum, and S. enterica Typhimurium showed an identical electrophoretic banding pattern and serological cross-reactions among each other. LPSs from wild-type Salmonella enteritidis and rough mutant S. gallinarum 9R were detoxified by cleavage of lipid A moieties using mild acid hydrolysis. The non-toxic saccharide moieties from both strains were coupled directly to bovine serum albumin (BSA). The conjugates were injected in mice in combination with monophosphory lipid A (MPL), Freund, and Alum adjuvants. The highest IgM and IgG titres were obtained when the conjugates were emulsified with MPL adjuvant, followed by Freund adjuvant. The antisera raised against the conjugates in combination with MPL and Freund adjuvants showed high complement-mediated lysis to the homologous strains. A correlation was observed between IgG titres and bactericidal activities against homologous strains. Low in vivo protection was obtained when mice immunized with the conjugates were challenged with 10 times the LD50 of the wild S. enteritidis.