Abstract:
Typhoid fever caused by Salmonella enterica serovar Typhi (S.Typhi) continues to be a major problem,
especially in developing countries. Due to the rapid emergence of multi-drug-resistant (MDR) strains,
which limits the efcacy of conventional antibiotics as well as problems associated with the existing
vaccines, eforts are being made to develop efective prophylactic agents. CdtB subunit of typhoid
toxin was selected for assessing its vaccine potential due to its high conservation throughout the
Typhi strains. In-vitro assessment of DNase activity of cloned and purifed CdtB protein showed a
signifcant decrease in the band intensity of DNA. The measure of metabolic activity and morphological
alterations assessed using diferent cell lines in the presence of CdtB protein showed no signifcant
signs of toxicity. These observations were further strengthened by cell cycle analysis, assessed by fow
cytometry. Keeping these observations in mind, the immunoprotective potential of CdtB was assessed
using S.Typhi induced mouse peritonitis model. A signifcant titer of IgG antibodies (>128000) against
CdtB protein was recorded in the immunized mice by enzyme-linked immunosorbent assay (ELISA),
which was also validated by immunoblotting. Active immunization with the protein protected 75%
mice against a lethal dose of S.Typhi Ty2. The data indicated a signifcant (up to 5log) reduction in the
bacterial load in the spleen and liver of immunized-infected mice compared to control (unimmunizedinfected) mice which might have resulted in the modulation of histoarchitecture of spleen and liver and
the levels of cytokines (IL-6, TNF-α and IL-10) production; thereby indicating the efectiveness of the
subunit. The observations deduced from the study give the proof of concept of immunogenic potential
of protein. However, further studies involving the immunoreactivity of CdtB with the statistically
signifcant number of sera samples obtained from the human patients would be helpful in establishing
the relevance of CdtB protein in humans and for making the strategies to develop it as an efective
vaccine candidate.
