Pathogenicity of ABC transporter SSU05_0946 of Streptococcus suis serotype 2

Objective To construct a mutant strain of Streptococcus suis type 2 05ZYH33 expressing ABC transporter SSU05_0946 and to study the pathogenicity of ABC transporter SSU05_0946 for better understanding the immune evasion strategies by Streptococcus suis. Methods Genome of the Streptococcus suis type 2 05ZYH33 strain was extracted and used as a template to amplify SSU05_0946 upstream and downstream homeodomains. Chloramphenicol-resistance gene was amplified by using pSET1 plasmid as the template. These three amplified fragments were fused and integrated with the thermo-sensitive plasmid pSET4s by using overlap extension PCR. Homologous recombination method was used to construct the mutant strain 05ZYH33Δ0946. Differences between the mutant and wild type strains were evaluated through bacterial adhesion assay, whole blood killing assay and challenge test in mice and piglets. Results The mutant strain 05ZYH33Δ0946 was successfully constructed. Results of bacterial adhesion assay demonstrated that SSU05_0946 was not involved in the adherence of Streptococcus suis to human epithelial cells. SSU05_0946 was an ovel anti-phagocytic factor and virulence factor of Streptococcus suis. Conclusion Streptococcus suis type 2 ABC transporter SSU05_0946 is a newly discovered virulence factor of Streptococcus suis, playing an important role in the evasion of host innate immunity by Streptococcus suis. Key words: Streptococcus suis type 2; Whole blood killing; Gene knockout; Virulence factor