Salmonella porins induce a sustained, lifelong specific bactericidal antibody memory response

We examined the ability of porins from Salmonella enterica serovar typhi to induce a long-term antibody response in BALB/c mice. These porins triggered a strong lifelong production of immunoglobulin G (IgG) antibody in the absence of exogenous adjuvant. Analysis of the IgG subclasses produced during this antibody response revealed the presence of the subclasses IgG2b, IgG1, IgG2a and weak IgG3. Despite the high homology of porins, the long-lasting anti-S. typhi porin sera did not cross-react with S. typhimurium. Notably, the antiporin sera showed a sustained lifelong bactericidal-binding activity to the wild-type S. typhi strain, whereas porin-specific antibody titres measured by enzyme-linked immunosorbent assay (ELISA) decreased with time. Because our porin preparations contained the outer membrane proteins C and F (OmpC and OmpF), we evaluated the individual contribution of each porin to the long-lasting antibody response. OmpC and OmpF induced long-lasting antibody titres, measured by ELISA, which were sustained for 300 days. In contrast, although OmpC induced sustained high bactericidal antibody titres for 300 days, postimmunization, the bactericidal antibody titre induced by OmpF was not detected at day 180. These results indicate that OmpC is the main protein responsible for the antibody-mediated memory bactericidal response induced by porins. Taken together, our results show that porins are strong immunogens that confer lifelong specific bactericidal antibody responses in the absence of added adjuvant.     

rOmpF and OMVs as efficient subunit vaccines against Salmonella enterica serovar Enteritidis infections in poultry farms

Salmonella enterica serovar Enteritidis remains the most prevalent serotype causing human salmonellosis through the consumption of contaminated foods, especially poultry products. The development of a subunit vaccine against S. Enteritidis can not only protect chickens against Salmonella infection in the poultry industry but also cut the transmission sources. In this study, both the expressed recombinant outer membrane protein F (rOmpF) and extracted outer membrane vesicles (OMVs) were developed as subunit vaccines against S. Enteritidis challenge in chickens. Immunization with the subunit vaccine could induce not only antibody production but also strong cell-mediated immune response. Both rOmpF plus QuilA adjuvant and OMVs alone had highly protective efficacy against S. Enteritidis challenge and rapidly decreased the colonization of bacteria in chicken. These findings revealed the potential application of rOmpF and OMVs as subunit vaccines in the poultry industry.