Orphan response regulator CovR plays positive regulative functions in the survivability and pathogenicity of Streptococcus suis serotype 2 isolated from a pig

Background: Streptococcus suis serotype 2 (S. suis 2) is an important zoonotic pathogen. Orphan response regulator CovR plays crucial regulative functions in the survivability and pathogenicity of S. suis 2. However, research on the CovR in S. suis 2 is limited.

Results: In this study, the regulative functions of CovR in the survivability and pathogenicity were investigated in S. suis 2 isolated from a diseased pig. The deletion of CovR significantly weakened the survivability and pathogenicity of S. suis 2. Compared with the wild-type strain, ΔcovR showed slower growth rates and thinner capsular polysaccharides. Moreover, ΔcovR showed reduced adhesion and invasion to Hep-2 cells as well as anti-phagocytosis and anti-killing ability to 3D4 cells and anti-serum killing ability. In addition, the deletion of CovR significantly reduced the colonisation ability of S. suis 2 in mice. The survival rate of mice infected with ΔcovR was increased by 16.7% compared with that of mice infected with S. suis 2. Further, the deletion of CovR led to dramatic changes in metabolism-related pathways in S. suis 2, five of those, including fructose and mannose metabolism, glycerolipid metabolism, ABC transporters, amino sugar and nucleotide sugar metabolism and phosphotransferase system, were significantly down-regulated.

Conclusions: Based on the results, CovR plays positive regulative functions in the survivability and pathogenicity of S. suis 2 SC19 strain isolated from a pig.