Immunogenicity of an autogenous Streptococcus suis bacterin in preparturient sows and their piglets in relation to protection after weaning.

Streptococcus suis is an important porcine pathogen causing meningitis and other invasive diseases in piglets of different ages. Application of S. suis serotype 2 bacterins to specific-pathogen-free (SPF) weaning piglets has been demonstrated to protect against the homologous serotype. However, autogenous S. suis bacterins are also applied to sows and suckling piglets in the field. Therefore, comparative evaluation of different bacterin immunization regimes, including sow vaccination, was performed in this study. The main objectives were to determine the immunogenicity of an S. suis bacterin in sows prepartum and its influence on active immunization of piglets. Experimental infection of 6- and 8-week-old weaning piglets was performed to elucidate protective efficacies. Humoral immune responses were investigated by an enzyme-linked immunosorbent assay (ELISA) measuring muramidase-released protein (MRP)-specific IgG titers and by opsonophagocytosis assays. Bacterin application elicited high MRP-specific IgG titers in the serum and colostrum of sows, as well as opsonizing antibodies. Piglets from vaccinated sows had significantly higher MRP-specific titers than respective piglets from nonvaccinated sows until 6 weeks postpartum. Vaccination of suckling piglets did not result in high MRP-specific titers nor in induction of opsonizing antibodies. Furthermore, neither vaccination of suckling nor of weaning piglets from immunized sows was associated with a prominent active immune response and protection at 8 weeks postpartum. However, protection was observed in respective 6-week-old weaning piglets, most likely because of protective maternal immunity. In conclusion, this study provides the first results suggesting protective passive maternal immunity for S. suis serotype 2 after bacterin vaccination of sows and a strong inhibitory effect on active immunization of suckling and weaning piglets, leading to highly susceptible growers.

Intranasal immunization with a live Streptococcus suis isogenic ofs mutant elicited suilysin-neutralization titers but failed to induce opsonizing antibodies and protection.

In Europe, Streptococcus suis serotypes 2 and 9 are very important causative agents of meningitis, arthritis and septicemia in piglets. So far, no vaccine has been described which elicits protection against both serotypes. The working hypothesis of this study was that an isogenic serotype 2 mutant attenuated in virulence but not in colonization of the respiratory tract might induce protective immunity against both serotypes. Piglets were immunized with the attenuated S. suis serotype 2 strain 10Deltaofs2/12, which is deficient in expression of the serum opacity factor OFS. Three weeks after intranasal application of 10Deltaofs2/12 piglets were challenged intravenously with two strains representing the most important S. suis pathotypes in Europe, the homologous MRP+ EF+ SLY+ serotype 2 strain and a heterologous MRP* SLY+ serotype 9 strain. Application of the live vaccine elicited significant serum IgG responses against muramidase-released protein (MRP), extracellular factor (EF) and, most prominently, suilysin. Seroconversion against suilysin was accompanied with an increase of suilysin-neutralization titers in the vaccinated group. Though mortality was lower in the vaccinated groups, significant protection was not observed, neither against the homologous nor against the heterologous challenge. This was in agreement with the finding that the vaccinated piglets had low opsonizing antibody titers insufficient to mediate elimination of the two challenge strains by porcine neutrophils. In conclusion, a single intranasal application of the S. suis serotype 2 strain 10Deltaofs2/12 elicited humoral immune responses against different S. suis antigens but failed to induce sufficient opsonizing antibody titers and protective immunity against systemic serotypes 2 and 9 challenges.

Streptococcus suis bacterin and subunit vaccine immunogenicities and protective efficacies against serotypes 2 and 9.

Streptococcus suis causes numerous diseases in pigs, most importantly, meningitis, arthritis, septicemia, and bronchopneumonia. One of the major problems in modern swine production is the lack of a vaccine protecting against more than one S. suis serotype. The objective of this study was to determine the protective efficacy of a serotype 2 murein-associated protein (MAP) fraction subunit vaccine in comparison to that of a bacterin against experimental challenge with serotype 2 (containing muramidase-released protein [MRP], extracellular factor, and suilysin [SLY]) and serotype 9 (containing MRP variant MRP* and SLY) strains. MAP was shown to include different surface-associated proteins, such as the MRP and surface antigen one (SAO) expressed by both pathotypes used for challenge. The results of this study demonstrated that the serotype 2 bacterin induced protective immunity against homologous challenge. In contrast, the protective efficacy of the MAP subunit vaccine was low, though MAP immunization resulted in high serum immunoglobulin G2 titers against MRP and SAO. Importantly, immunization with bacterin but not with MAP induced opsonizing antibody titers against the serotype 2 strain, and these antibody titers were found to correlate with protection. However, after absorption with a nonencapsulated isogenic mutant, the sera from bacterin-immunized piglets failed to facilitate neutrophil killing, indicating that antibodies directed against capsule may not have been essential for opsonophagocytosis. Furthermore, induction of opsonizing antibodies against serotype 9 was not detectable in the group receiving bacterin or in the group receiving the MAP vaccine. In agreement, protection against the heterologous serotype 9 strain was low in both groups. Thus, identification of an antigen protecting against these two important S. suis pathotypes remains an important goal of future studies.