Fusion protein of Salmonella typhi flagellin as antigen for diagnosis of typhoid fever.

SUMMARY We previously established the specific 52 kDa antigen of Salmonella Iyphi, detected by our monoclonal antibodies, which was a flagellln protein. Com· parison of the nucleotide sequences of phase-1 flagellin of Salmonella species available through GenBank database showed high homology at both ends of the genes with lower degree of homology in the middle portion which contained the antigenically variable regions. Thus, proteins from the central regions of flagellin genes should be species specific and could be used as specific antigens for the Immunodiagnostic tests. In this report, recombinant protein derived from the central region of S.lyphi flagellln was produced as a fuSion protein with glutathlone-5-transferase. This fusion protein was used as specific S.lyphi antigen for the Irrmunodiagn ostlc test to detect IgM antibodies in sera using enzyme-linked immunosorbent assay. The sensitivity, speci­ ficity, accuracy, positive predictive value and negative predictive value of this test were 53.5, 98.0, 91.5, 82.1 and 92.4%, respectively. typhimurium, Escherichia coli, Pseudomonas pseudomallei and Yersinia enterocolitica}. I We also demonstrated by SDS-PAGE and Western blot using S. typhi whole cell antigen to show the presence of specific IgM antibody to the 52 kDa protein in sera from patients with acute typhoid infection. The result suggested that the 52 kDa protein of S. typhi was a strong immunogen and could be used to diagnose the speci fic antibodies in sera . Because of this evidence, we tried to develop a diagnostic test detecting JgM antibodies against S. typhi specific antigen(s) from sera of the patients.