Abstract
The variable 56-kDa major outer membrane protein of Orientia tsutsugamushi is the immunodominant antigen in human scrub typhus infections. The gene encoding this protein from Karp strain was cloned into the expression vector pET11a. The recombinant protein (r56) was expressed as a truncated nonfusion protein (amino acids 80 to 456 of the open reading frame) which formed an inclusion body when expressed in Escherichia coli BL21. Refolded r56 was purified and compared to purified whole-cell lysate of the Karp strain of O. tsutsugamushi by immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) for reactivity with rabbit sera prepared against eight antigenic prototypes of O. tsutsugamushi as well as several other species of Rickettsiales and nonrickettsial antigens. Refolded r56 exhibited broad reactivity with the rabbit antisera against the Orientia prototypes, and the ELISA reactions with the r56 and Karp whole-cell lysate antigens correlated well (r = 0.81, n = 22, sensitivity compared to that of standard ELISA of 91%). Refolded r56 did not react with most antisera against other rickettsial species or control antigens (specificity = 92%, n = 13) using a positive cutoff value determined with eight uninfected rabbit sera. Refolded r56 was evaluated further by ELISA, using 128 sera obtained from patients with suspected scrub typhus from Korat, Thailand, and 74 serum specimens from healthy Thai soldiers. By using the indirect immunoperoxidase assay as the reference assay, the recombinant antigen exhibited a sensitivity and specificity of 93% or greater for detection of both IgG and IgM in the ELISA at 1:400 serum dilution. These results strongly suggest that purified r56 is a suitable candidate for replacing the density gradient-purified, rickettsia-derived, whole-cell antigen currently used in the commercial dipstick assay available in the United States.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
