Serodiagnostic evaluation of recombinant CdtB of S. Typhi as a potential candidate for acute typhoid

Abstract

Typhoid fever caused by human restricted Salmonella typhi presents a considerable health burden on developing South-Asian nations like India. The suboptimal sensitivity and specificity associated with culture-based isolation of etiological agent and the extensively used surface antigen-based serological assays often lead to misdiagnosis and inappropriate antimicrobial treatment. The increasing reports of the emergence of resistant strains and undefined disease burden signify the critical need for an inexpensive, reliable, easy-to-use, and highly sensitive diagnostic test for typhoid fever. Utilizing S. typhi-specific and immunogenic antigens in sero-diagnostic assays could lead to precise diagnosis of acute typhoid and prompt treatment. In this study, we report cloning, expression, and purification of recombinant Cytolethal distending toxin subunit B (CdtB) of S. typhi, which is reported to be highly specific, immunogenic, and expressed only upon S. typhi infection. We further evaluated the purified recombinant CdtB for its diagnostic potential in an IgM-based indirect ELISA format using 33 human samples. Twenty-one serum samples from blood culture confirmed cases (n = 21) of typhoid and 12 samples from healthy controls (n = 12) were tested. The assay showed sensitivity of 100% and specificity of 83.3% respectively with positive and negative predictive values of 91.3 and 100% respectively. Efficient detection of specific IgM antibodies indicates that CdtB could be highly valuable in sero-diagnosis of acute typhoid and rapid screening of clinical samples.

Prophylactic potential of cytolethal distending toxin B (CdtB) subunit of typhoid toxin against Typhoid fever

“…On completion of the incubation period, a substrate (TMB) 50 μl was added and allowed to develop color for 10 min in dark. The reaction was stopped with 50 μl/well of 0.1 N H 2 SO 4 , and the plate was read at 450 nm with a microplate reader 32,33 .…”

“…The membrane was washed every time with wash buffer (PBS-T, 0.05%) and then incubated with anti-human IgG-HRP conjugated antibody (1: 20000 dilution) for 1 h at 37 °C. After this, the membrane was developed with chromogenic TMB solution (in the dark) for 10–15 min and the reaction was stopped by washing with wash buffer 32 .…”

Salmonella Typhoid Toxin PltB Subunit and Its Non-typhoidal Salmonella Ortholog Confer Differential Host Adaptation and Virulence

“…In humanized mice engrafted with human fetal liver stem and progenitor cells that partially supported S. Typhi survival and replication, typhoid toxin contributed significantly to the establishment of persistent infection by its tropism to immune cells (Song et al, 2010;Yang et al, 2018b). Several clinical reports have shown the abundant presence of anti-CdtB antibodies in the sera of recovered typhoid patients, indicating that S. Typhi produces typhoid toxin during infection in humans (Charles et al, 2014;Liang et al, 2013;Sharma et al, 2018;Tran Vu Thieu et al, 2017). Primary human cells and tissues relevant to typhoid signs express the specific glycan receptor moieties for typhoid toxin, implying that typhoid toxin can target these cells during human infection (Yang et al, 2018b).…”

The role of 9-O-acetylated glycan receptor moieties in the typhoid toxin binding and intoxication

“…When administered to laboratory animals, typhoid toxin recapitulates many of the severe acute-phase symptoms of typhoid fever, such as lethargy, malaise, and stupor (the meaning of typhos in Greek), along with leukopenia and neurologic complications [10,11]. A majority of typhoid fever patients exhibit high titers of anti-typhoid toxin antibodies in their sera [12][13][14][15]. Primary human cells and tissues relevant to typhoid clinical signs and symptoms express the specific glycan receptor moieties for typhoid toxin [11], although whether at least some of the glycan receptor moieties are further modified by additional chemical groups has not been revealed.…”