Laboratory Diagnosis of Paratyphoid Fever: Opportunity of Surface Plasmon Resonance

Abstract

Paratyphoid fever is caused by the bacterium Salmonella enterica serovar Paratyphi (A, B and C), and contributes significantly to global disease burden. One of the major challenges in the diagnosis of paratyphoid fever is the lack of a proper gold standard. Given the absence of a licensed vaccine against S. Paratyphi, this diagnostic gap leads to inappropriate antibiotics use, thus, enhancing antimicrobial resistance. In addition, the symptoms of paratyphoid overlap with other infections, including the closely related typhoid fever. Since the development and utilization of a standard, sensitive, and accurate diagnostic method is essential in controlling any disease, this review discusses a new promising approach to aid the diagnosis of paratyphoid fever. This advocated approach is based on the use of surface plasmon resonance (SPR) biosensor and DNA probes to detect specific nucleic acid sequences of S. Paratyphi. We believe that this SPR-based genoassay can be a potent alternative to the current conventional diagnostic methods, and could become a rapid diagnostic tool for paratyphoid fever.

Keywords: SPR; Salmonella Paratyphi; bacterial detection; biosensor; optical sensor; paratyphoid fever.

Figure 1

The general procedure for the Widal test tube method [44]. 1. An essential step in any Widal test procedure is the serial dilution (the number of folds could be varied). This helps to avoid false negative results, due to Prozone phenomenon (high antibody (Ab) titer compared to the number of antigens (Ag)); 2. Reagents containing specific S. enterica serovars antigens are added. Although the test relies on the antigenic structure of each serovar (Table 1), the O somatic Ag of S. Paratyphi is not used, because of the factor 12 that is also present in the O Ag of S. Typhi; 3. Upon addition of Ags, the setup is properly mixed and then incubated. Usually, the duration of incubation is up to 18 h at 37 °C; 4. After incubation, the sample is vortexed and then agglutination is viewed by the naked eye if the result is positive. The final result is the highest dilution (titer) with a visible agglutination.

Figure 2

A schematic representation of surface plasmon resonance (SPR) biosensor based on antibody/antigen binding. This SPR system is commonly used for bacterial detection. Before the bindings occur, the angle of reflection is at I, and after the analyte (Ag) binds to the immobilized ligand (Ab), the reflection angle widens, due to the increase in refractive indices on the gold surface [96].

Figure 3

Annual publications on the SPR-based methods in the last two decades, according to PubMed databases (as at 20 March 2020).

Figure 4

A proposed SPR-based genoassay to detect S. Paratyphi. Immobilization of biotinylated DNA probe onto the gold surface can be done, based on the cross-linking (capturing) method. Streptavidin will be functionalized with biotin (coupled with DNA probe) as a protein capture agent. The binding of the immobilized biotinylated DNA probe to ssDNA will produce a specific change in the light output reflected from the gold-based surface. By monitoring both the immobilization process, as well as the reaction between the biotinylated DNA probe and ssDNA, the changes in refractive index, absorbance, reflectance, kinetic, binding assay, and spectrum can be obtained and analyzed, allowing the determination of the most sensitive parameter within this approach.