Diagnostic potential of recombinant SucB protein for tularemia: An ELISA approach

Serological methods are key for tularemia diagnosis. This study evaluated the recombinant SucB protein of Francisella tularensis as a potential antigen for tularemia serodiagnosis using an enzyme-linked immunosorbent assay ELISA.

The succinyltransferase dihydrolipoamide protein (SucB, FTT0077) was selected based on previous studies identifying immunodominant antigens of F. tularensis. The SucB gene was amplified from F. tularensis subsp. holarctica LVS (NCTC 10857), cloned into the pET28a expression vector, and expressed in Escherichia coli BL21 (DE3). Recombinant protein expression was confirmed by SDS-PAGE and Western blot. Immunoblotting with sera from tularemia patients and controls demonstrated strong SucB immunoreactivity. Based on this, a SucB-based ELISA was developed and optimized.

The recombinant SucB protein demonstrated strong immunoreactivity with sera from tularemia-positive patients, with minimal cross-reactivity in controls. Receiver operating characteristic (ROC) analysis identified an optimal optical density (OD) cut-off of 0.27 for anti-F. tularensis IgG detection. At this cut-off, the assay showed a sensitivity of 96.8% (95% CI: 93.3-100%) and a specificity of 98.8% (95% CI: 96.7-100%). The positive predictive value (PPV) and negative predictive value (NPV) were 98.92% and 96.59%, respectively, indicating robust diagnostic performance. Agreement analysis demonstrated excellent concordance between the SucB-based ELISA and a commercial diagnostic kit, with a Cohen's kappa coefficient of 0.96, reflecting near-perfect agreement.

This study highlights recombinant SucB as a promising biomarker for tularemia diagnosis. SucB-based ELISA could improve detection, especially in endemic or resource-limited areas. Further research with larger groups is needed to confirm these results.