Abstract
The increase in Salmonella Enteritidis (SE) human outbreaks, mostly incriminating the poultry as the source of the infection, has increased the search to control this pathogen in chickens. The purpose of this study was to quantify the SE fimbriae (SEF)-specific serum and egg yolk antibodies following a controlled SE-challenge of laying hens previously immunized with a newly developed live SE vaccine versus a classical killed commercial vaccine. This work also aimed to determine the relationship between this quantitative assessment and the protection against SE invasiveness in the livers and spleens of the experimental hens. In the procedure, laying hens were divided into 4 different groups. Birds in group A were given orally a newly developed live SE vaccine at 222 days of age, while birds in group D were given subcutaneously in the neck a commercial killed SE vaccine at 40 and 130 days of age; birds of groups B and C were deprived of vaccination (control groups). Hens in groups A, B, and D were challenged orally at 237 days of age with a highly invasive SE strain, acquiring 14.1 and similar to 50 kb plasmids, at 1.5 x 10(11) cfu/hen, while birds in group C were left without challenge. On one hand, the vaccinated-challenged groups A and D and unvaccinated-challenged group B showed quantitative serum antibodies specific to SE fimbriae SEF 14 and SEF 21, and egg yolk antibodies specific to SEF 21 at 7 days post challenge. On the other hand, only the live SE vaccinated-challenged group A showed quantitative egg yolk antibodies-specific to SEF 14 at 7 days post challenge. The SEF 14- and SEF 21-specific serum antibodies decayed consistently at 14 days post challenge in groups A, B, and D. On the contrary, there was an increase in egg yolk antibodies in groups A, B, and D specific to SEF 14 and a decrease to SEF 21 at 14 days post challenge. The highest level of SEF 14- and SEF 21 -specific egg yolk antibodies at 7 and 14 days post challenge were recognized in group A administered the newly developed live SE vaccine; while hens of group D administered the killed SE vaccine had the highest level of SEF 14- and SEF 2 1 specific serum antibodies at 7 and 14 days post challenge. Hens in groups A and D did result in 100% protection against invasiveness of SE to livers and spleens. However, SE-challenged hens of group B, deprived of live or killed vaccine, showed a 40% and 20% invasiveness in the livers and spleens, respectively. The controlled unvaccinated and unchallenged group C didn't show any infection in livers or spleens by SE.