RESUMEN
We report experiments in which high quality silica opal films are used as three-dimensional hypersonic crystals in the 10 GHz range. Controlled sintering of these structures leads to well-defined elastic bonding between the submicrometer-sized silica spheres, due to which a band structure for elastic waves is formed. The sonic crystal properties are studied by injection of a broadband elastic wave packet with a femtosecond laser. Depending on the elastic bonding strength, the band structure separates long-living surface acoustic waves with frequencies in the complete band gap from bulk waves with band frequencies that propagate into the crystal leading to a fast decay.
RESUMEN
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.