RESUMEN
The role of Vi-capsular polysaccharide [Vi-CPS] in human immunity against infection caused by Salmonella typhi is well known. The downstream process of purification generally causes depolymerization of Vi-CPS to a nonimmunogenic low molecular weight form. In the present study, a standard strain of Sal. typhiTy6s was grown under submerge cultural conditions in a pilot-plant scale of 90 liter fermentor. At the late exponential growth phase, crude polysaccharide was obtained from fermentation broth by detergent-phenol extraction method and purified by ultracentrifuge differentiation technique. Analytical data reveals that by optimization of fermentation parameters, not only was the yield of production increased from 1.6 mg/L to 4.9 mg/L, but also the polysaccharide retained its native molecular stability and immunogenicity. Therefore, purified Vi-CPS can be regarded as a reliable immunogen to control typhoid fever in man