Abstract
Streptococcus (S.) suis is one of the most important pathogens in pigs causing meningitis, arthritis, endocarditis and serositis. Furthermore, it is also an emerging zoonotic agent. In our previous work we identified a highly specific IgM protease in S. suis, designated IdeSsuis. The objective of this study was to characterize the function of IdeSsuis in the host-pathogen interaction. Edman-sequencing revealed that IdeSsuis cleaves the heavy chain of the IgM molecule between constant domain 2 and 3. As the C1q binding motif is located in the C3 domain, we hypothesized that IdeSsuis is involved in complement evasion. Complement-mediated hemolysis induced by porcine hyperimmune sera containing erythrocyte-specific IgM was abrogated by treatment of these sera with recombinant IdeSsuis. Furthermore, expression of IdeSsuis reduced IgM-triggered complement deposition on the bacterial surface. An infection experiment of prime-vaccinated growing piglets suggested attenuation in the virulence of the mutant 10ΔideSsuis. Bactericidal assays confirmed a positive effect of IdeSsuis expression on bacterial survival in porcine blood in the presence of high titers of specific IgM. In conclusion, this study demonstrates that IdeSsuis is a novel complement evasion factor, which is important for bacterial survival in porcine blood during the early adaptive (IgM-dominated) immune response.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0171-6) contains supplementary material, which is available to authorized users.
Highlights
Streptococcus (S.) suis colonizes different mucosa of pigs, its main host
Suppurative meningitis caused by S. suis is one of the most important diseases in modern swine production as it is associated with severe economic losses
Expression of IdeSsuis reduces IgM-triggered complement deposition on the bacterial surface of an unencapsulated mutant We investigated deposition of C3 on the surface of opsonized S. suis strains by flow cytometry to further investigate the hypothesis that IdeSsuis is involved in complement evasion
Summary
Streptococcus (S.) suis colonizes different mucosa of pigs, its main host. Cross the mucosal barrier, cause bacteremia and infect various tissues leading to severe pathologies, such as meningitis, arthritis, endocarditis and serositis. Suppurative meningitis caused by S. suis is one of the most important diseases in modern swine production as it is associated with severe economic losses. S. suis exhibits a high degree of diversity among and within different serotypes. Serotype 2 is worldwide the most important serotype isolated from affected tissues in piglets and an important zoonotic agent [1,2,3]. Numerous proteins involved in interaction with the host have been functionally characterized [4,5]. We identified a 124 kDa large Immunoglobulin M-degrading enzyme of S. suis, designated IdeSsuis [6].
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