The two-component regulatory system CiaRH contributes to the virulence of Streptococcus suis 2.

Two-component regulatory systems (TCSs) are widely distributed among bacteria and enable the organisms to make coordinated changes in gene expression in response to a variety of environmental stimuli. In this work, we constructed a mutant strain of the TCS CiaRH and measured its virulence in vitro and in vivo. Compared with the wild type strain, the mutant strain exhibited a significant decrease in adherence to epithelial cells Hep-2 and PIEC. Furthermore, the deletion of CiaRH not only enhanced the bactericidal activity of RAW264.7 macrophage against Streptococcus suis 2, but also increased blood clearance of S. suis 2 in vivo. More importantly, the mutant was attenuated in vivo in CD1 mice and pigs, with reduced mortality, morbidity and impaired bacterial growth observed in specific organs. These results suggest that the CiaRH is required for S. suis 2 virulence.