Evaluation of the recombinant protein Tp0965 of Treponema pallidum as candidate antigen for serological diagnosis of syphilis

Abstract

Backgraund: Treponemal tests based on detection of antibodies against the T. pallidum antigens are the most specific methods for serological diagnosis of syphilis. Due to inability to cultivate this bacterium in vitro, the most promising sources of its antigens for diagnostic reactions are recombinant proteins of T. pallidum. Cloning and evaluation of the analytical value of certain T. pallidum proteins is the approach to improve the sensitivity, specificity, and reproducibility of serological tests for syphilis, including possibilities of differential diagnosis of various forms of the disease.Objective: The aim of present study was to evaluate the analytical values (sensitivity and specificity) of Tp0965 recombinant protein of T. pallidum as a candidate antigen for serological diagnosis of syphilis.Methods: Tp0965 gene was amplified by polymerase chain reaction from T. pallidum genomic DNA (Nichol's strain) and the nucleotide sequence was cloned into the expression vector pET28a. E. coli BL-21 (DE3) cells were transformed with this plasmid, and the recombinant protein production was induced by isopropyl-β-D-1-thiogalactopyranoside. Isolation and purification of Tp0965 recombinant protein from bacterial lysate was performed by metal‐chelate affinity chromatography using Ni-NTA Sepharose. The collected protein was seeded on high binding 96-well plates, which were used for ELISA with sera of patients with various forms of syphilis in comparison with healthy donors.Results: High frequency of positive ELISA results was shown with serum of patients with syphilis, compared with a group of healthy donors. The sensitivity of serological reactions using recombinant protein Tr0965 was 98.8%, specificity - 87.5%. The highest sensitivity (100%) was detected in the groups of patients with primary, secondary and early latent syphilis, while in the group of patients with late latent syphilis it decreased to 95.2%.Conclusions: We concluded that due to their specificity the recombinant protein Tp0965 T.pallidum can be used as a candidate antigen for development of syphilis serological diagnostic assays.