Immunogenicities of vaccines including the immunoglobulin M-degrading enzyme of Streptococcus suis, rIdeSsuis, and protective efficacy against serotype 14 in piglets

Streptococcus suis (S. suis) is a major porcine pathogen. Some strains have a substantial zoonotic potential such as serotype (cps) 14 as the second most important cps in human infections. To this date no licensed S. suis vaccine is available in Europe though subunit vaccines and bacterins have been examined by several scientific groups worldwide. Objectives of this study were to determine protective efficacy of rIde_Ssuis vaccination against intranasal S. suis cps14 challenge in conventional weaned piglets and to investigate additionally immunogenicity of rIde_Ssuis vaccination in cesarean-derived colostrum-deprived (CDCD) piglets. Immunization led to reduction of bacterial multiplicity in porcine blood and delayed onset of clinical signs of cps14 disease in conventional rIde_Ssuis-vaccinated piglets. However, significant differences were not recorded which might be related to comparable low anti-Ide_Ssuis antibody levels and insufficient neutralization of IgM protease activity in this animal experiment. In contrast, immunization of cesarean-derived colostrum-deprived piglets with rIde_Ssuis resulted in high α-rIde_Ssuis IgG antibody levels and a highly significant reduction of the survival factor of the cps14 challenge strain in porcine blood in vitro. In conclusion, the results of this study indicate bactericidal immunity against S. suis cps14 by Ide_Ssuis specific immunity.