Abstract

Typhoid poses a global public health concern. Presently available vaccines against typhoid have certain drawbacks that make them unsuitable for mass immunization, especially to children and elderly people. The outer membrane proteins (OMPs) of Salmonella have strong potential for the development of a candidate subunit vaccine against typhoid. We previously reported that a 49 kDa OMP confers protection against experimental salmonellosis. In the present study we report the cloning, expression of a recombinant protein to evaluate its potential to elicit an immune response against a challenge with Salmonella. The gene encoding the 49 kDa Salmonella typhi protein was cloned in a bacterial expression plasmid pQE-60 under the control of an IPTG induciblelac promoter and high-level expression of the 447 amino acid long protein with 6xHis tag was achieved in Escherichia coli strain SG 13009. The recombinant protein was purified to homogeneity by a single step Ni-NTA affinity. The yields of expressed protein were ~26 mg/L. The immunogenic evaluation of the recombinant protein vis-a-vis its native counterpart in S. typhi and Salmonella typhimurium was carried out using protection studies, bacterial clearance from erythropoitic system, cell-mediated immunity and antibody response. The immungenecity of the r-protein is comparable to 49 kDa proteins from S. typhi and S. typhimirium. These results may provide keen insights into the development of a conjugate-subunit vaccine against typhoid.

Key words: Outer membrane protein, expression, salmonella, typhoid, vaccine.