Characterization Studies on the sugC Gene of Streptococcus suis Serotype 2 in Adhesion, Invasion, and Virulence in Mice

The <i>sugC</i> gene of <i>Streptococcus suis</i> (<i>S. suis</i>) is a coding gene for the ATP-binding transporter-associated protein with strong pathogenicity. In order to reveal the effect of the <i>sugC</i> gene on the virulence of <i>S. suis</i> serotype 2, a wild-type strain of TJS75, isolated from fattening pigs' brain tissue samples, was used as a parent strain, and a knockout <i>sugC</i> gene (Δ<i>sugC</i>) and complementary strain (CΔ<i>sugC</i>) were successfully constructed via homologous recombination technology. The biological characteristics of TJS75, Δ<i>sugC</i> and CΔ<i>sugC</i> were compared and analyzed through growth curves, biochemical characteristics, hemolysis characteristics, cell infection tests and pathogenicity tests on BALB/c mice. The results of the growth characteristic experiments in vitro showed that the plateau stage growth period of Δ<i>sugC</i> was delayed compared to the TJS75 strain, but there was no difference in the total number of bacteria. The biochemical characteristics and hemolysis ability of Δ<i>sugC</i> in sheep blood had no difference compared with TJS75, but its adhesion and invasion abilities in PK-15 cells were decreased. Knockout of the <i>sugC</i> gene had no impact on the expression levels of adhesion-related genes in TJS75 in real-time PCR analysis. In addition, the LD₅₀ of Δ<i>sugC</i> in BALB/c mice was 1.47 × 10⁸ CFU, seven times higher than that of TJS75 (LD₅₀ = 2.15 × 10⁷ CFU). These results illustrate that the deletion of <i>sugC</i> reduced the virulence of TJS75 to BALB/c mice, but its role in the adhesion and invasion of PK-15 cells in this strain needs to be further explored. In summary, this study provides evidence that the <i>sugC</i> gene is a virulence-related gene in the <i>S. suis</i> serotype 2 strain and plays a crucial role in the adhesion and invasion of <i>S. suis</i>. This study lays a foundation for the further exploration of the potential virulence factors and pathogenesis of <i>S. suis</i>.