Recombinant Extracellular Factor Protein of Streptococcus suis as Potential Candidate Protein for Antibodies Against S. suis Detection and Subunit Vaccine Development: In Silico and In Vitro Approaches

<b>Background/Objectives</b>: <i>Streptococcus suis</i> is a zoonotic pathogen that causes infections in pigs and humans, leading to significant economic losses. <i>S. suis</i> can evade the immune system of hosts and induce persistent infections. Early detection and vaccination are crucial for controlling the disease in swine industries. This study aimed to investigate candidate recombinant protein for antibodies against <i>S. suis</i> detection and subunit vaccine development. <b>Methods</b>: The whole genome of <i>S. suis</i> BM407 was analyzed using bioinformatic tools to predict suitable proteins and genes for recombinant protein expression. Partial extracellular factor protein (<i>epf</i>) genes of <i>S. suis</i> serotype 2 DMST18783 were amplified. A 3301 bp amplicon was digested, and a specific 615 bp fragment was inserted into a pQE81L-KAN vector. Then, the constructed plasmid was cloned and expressed in <i>Escherichia coli</i> DH10β. Purified protein was analyzed using SDS-PAGE. In addition, translated amino acid sequences were analyzed for immune response properties, molecular docking, molecular dynamic simulation, and epitope prediction. <b>Results</b>: The amino acid sequence of recombinant extracellular factor protein (rEF) was revealed as a promising antigen containing putative protective regions as linear epitopes. Furthermore, the rEF was expressed as a histidine-tagged recombinant protein, and its properties were nearly similar to the predicted rEF using bioinformatic tools. Binding of the recombinant EF (rEF) protein was found to reduce fluctuations in the swine toll-like receptor 2. Furthermore, the rEF contained several regions that were predicted to be epitopes for both B-cells and T-cells. <b>Conclusions</b>: This study indicates that the recombinant EF fragment is a promising candidate for detecting antibodies against <i>S. suis</i> and as a component of a subunit vaccine.