Characterization of a phase 1-d epitope on Salmonella typhi flagellin and its role in the serodiagnosis of typhoid fever

A monoclonal antibody (MAb) directed against Salmonella typhi 52 kDa flagel lin protein has been previously produced by our group. in this study, we ha ve demonstrated that the epitope specific to the MAb is unique to phase 1-d . To map the epitope, plasmids encoding different regions of S. typhi flage llin gene were constructed. Analysis of protein produced from each recombin ant plasmid indicated that the epitope specific to the MAb resided within a mino acids 171-303 (region IV) of S. typhi flagellin protein. The recombina nt region IV flagellin was used to develop an ELISA for the detection of Ig M antibody to S. typhi in serum. In the hemoculture-positive typhoid group, the developed ELISA was positive in 77 of 92 cases. In patients with non-t yphoidal Salmonella, gram-positive and gram-negative bacteria or dengue vir us, the ELISA was negative in all 78 cases. Two from 116 healthy control su bjects had positive reactions with the assay. The calculated sensitivity, s pecificity, positive and negative predictive values of the test were 83.7%, 99.0%, 97.5% and 92.8%, respectively. With such high validity together wit h the requirement of only a single serum specimen and one day for performin g the test, the developed ELISA should become a valuable diagnostic test fo r typhoid fever.