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

<i>Streptococcus suis</i> (<i>S. suis</i>) is a major porcine pathogen. Some strains have a substantial zoonotic potential such as serotype (<i>cps</i>) 14 as the second most important <i>cps</i> in human infections. To this date no licensed <i>S. suis</i> 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 _<i>Ssuis</i> vaccination against intranasal <i>S. suis cps</i>14 challenge in conventional weaned piglets and to investigate additionally immunogenicity of rIde _<i>Ssuis</i> 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 <i>cps</i>14 disease in conventional rIde _<i>Ssuis</i> -vaccinated piglets. However, significant differences were not recorded which might be related to comparable low anti-Ide _<i>Ssuis</i> antibody levels and insufficient neutralization of IgM protease activity in this animal experiment. In contrast, immunization of cesarean-derived colostrum-deprived piglets with rIde _<i>Ssuis</i> resulted in high α-rIde _<i>Ssuis</i> IgG antibody levels and a highly significant reduction of the survival factor of the <i>cps</i>14 challenge strain in porcine blood <i>in vitro</i>. In conclusion, the results of this study indicate bactericidal immunity against <i>S. suis cps</i>14 by Ide _<i>Ssuis</i> specific immunity.