The attenuated Salmonella typhimurium PhoPc strain is avirulent but immunogenic via the oral route in mice and is attenuated in survival in macrophage cell lines. In this study, the fate of PhoPc bacteria expressing green fluorescent protein was investigated in murine Peyer's patches. The survival of PhoPc was monitored after orogastric inoculation of BALB/c mice. Bacteria persisted for several weeks in the Peyer's patches and were also recovered from the mesenteric lymph nodes and spleen. Confocal microscopy analysis identified dendritic cells as the Peyer's patch cell type that internalized PhoPc expressing green fluorescent protein at early time points. In addition, live PhoPc were found in Peyer's patch dendritic cells and not in B cells 3 days after orogastric inoculation. Taken together, these results provide strong evidence that PhoPc is internalized and survives within Peyer's patch dendritic cells. As these cells are potent antigen-presenting cells, these data could explain the immunogenicity of S. typhimurium vaccine strains in vivo.

Serial passage of two infectious bronchitis virus (IBV) vaccine strains in chickens enhanced their capacity to increase the incidence and severity of Mycoplasma synoviae (MS) airsacculitis. Included in this report were the mild Massachusetts-type Connaught strain and the Arkansas 99 vaccine strain of IBV. The Connaught strain and one of two Ark 99 vaccine strains passaged in chickens increased the incidence of airsacculitis markedly compared with nonpassaged virus. The other Ark 99 vaccine virus already exacerbated MS airsacculitis, before passage in chickens, and its influence did not increase on passage. All IBV strains studied to date have either possessed this trait or reacquired it on passage in the natural host.

Broiler chicks were vaccinated subcutaneously in the neck at various ages with a single 0.5-ml dose of beta-propiolactone-inactivated Mycoplasma gallisepticum (MG) oil-emulsion bacterin. Four weeks later, vaccinated and control chicks were placed in cold environmental cabinets, infected with infectious bronchitis virus intratracheally, and 2 days later challenged by aerosol exposure to live MG broth culture. All chicks were killed 21 days later and scored postmortem for the rate and severity of airsacculitis produced in each group. Broiler chicks vaccinated at 1 day of age had only slight protection against the development of airsacculitis. Results were variable when chicks were vaccinated at 7 days of age, with little evidence of resistance to airsacculitis. However, when broiler chicks were vaccinated with MG bacterins at 11 to 15 days of age, they acquired significant protection against airsacculitis compared with controls. Viable MG organisms were readily isolated from most of the sampled tracheas and air-sac lesions cultured 21 days post-challenge, indicating a lack of protection against infection of the respiratory tract. MG-vaccinated chicks generally produced antibodies readily detectable by the rapid serum-plate test, tube-agglutination, and hemagglutination-inhibition (HI) tests. Some of the vaccinated chicks, but none of the unvaccinated control chicks, developed positive reactions to agar-gel-precipitin tests following challenge. Low HI titers at challenge were not necessarily indicative of lack of protection against the development of airsacculitis, since good protection was often observed in chickens with low to moderate HI titers.

Six groups of white leghorn pullets were studied to determine the ability of beta-propiolactone-inactivated Mycoplasma gallisepticum (MG) oil-emulsion bacterins to counteract reductions in egg production caused by MG infection. The pullets were inoculated with 0.5 ml of MG bacterin subcutaneously in the neck at about 20 weeks of age and were challenged with MG near 28 weeks of age, when they were in peak egg production. Various challenge schemes with infectious bronchitis virus were used at the time of MG challenge to increase the reduction in egg production. MG bacterins afforded protection against moderate drops in egg production in at least three of the studies, where the unvaccinated challenged control hens exhibited reduced egg production.