Preparation and evaluation of immunogenic conjugates of Salmonella enterica serovar Typhi O-specific polysaccharides with diphtheria toxoid

Hum Vaccin Immunother. 2012 Feb;8(2):189-93. doi: 10.4161/hv.18350. Epub 2012 Feb 1.


Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), is a major health problem particularly in developing countries. The available vaccines have certain limitations regarding their efficacy, and inability to induce an immune response especially in individuals under 2 years of age. Conjugate vaccines which consist of a bacteria-specific polysaccharide chemically bound to a carrier protein overcome these problems by inducing a T-cell dependent immune response characterized by enhanced immunogenicity in all ages. In this study, O-specific polysaccharides (OSP) of S. Typhi were conjugated to diphtheria toxoid (DT) using adipic acid dihydrazide (ADH) as a linker. These conjugates (OSP-AH-DT) were then evaluated for their immunogenicity using mice as a model and showed significantly higher levels of IgG ELISA titers (P = 0.0241 and 0.0245) than lipopolysaccharides alone. Different immunization schedules were compared and it was found that schedule-B (three injections with 4-weeks interval) induced higher immune responses than schedule-A (three injections with 2-weeks interval). We showed that diphtheria toxoid can be successfully employed as a carrier protein for conjugation with Salmonella OSP and play an important role in facilitating adequate immune response.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Bacterial / blood*
  • Antibodies, Bacterial / immunology
  • Carrier Proteins / immunology
  • Diphtheria Toxoid / chemistry
  • Diphtheria Toxoid / immunology*
  • Female
  • Immunization Schedule
  • Immunoglobulin G / biosynthesis
  • Mice
  • Mice, Inbred BALB C
  • O Antigens / chemistry
  • O Antigens / immunology*
  • Salmonella typhi / immunology*
  • Typhoid Fever / immunology
  • Typhoid Fever / prevention & control*
  • Typhoid-Paratyphoid Vaccines / chemistry
  • Typhoid-Paratyphoid Vaccines / immunology*
  • Vaccines, Conjugate / chemistry
  • Vaccines, Conjugate / immunology


  • Antibodies, Bacterial
  • Carrier Proteins
  • Diphtheria Toxoid
  • Immunoglobulin G
  • O Antigens
  • O-specific polysaccharide, Salmonella
  • Typhoid-Paratyphoid Vaccines
  • Vaccines, Conjugate