Evaluation of a Salmonella Strain Lacking the Secondary Messenger C-di-GMP and RpoS as a Live Oral Vaccine

• Published in: PloS one 2016-08, Vol.11 (8), p.e0161216-e0161216
• Main Authors: Latasa, Cristina, Echeverz, Maite, García, Begoña, Gil, Carmen, García-Ona, Enrique, Burgui, Saioa, Casares, Noelia, Hervás-Stubbs, Sandra, Lasarte, Juan José, Lasa, Iñigo, Solano, Cristina
• Format: Article
• Language: English
• Subjects: Administration, Oral; Analysis; Animals; Antibodies; Attenuation; Bacteria; Bacterial infections; Bacterial Proteins - physiology; Biofilms; Biology and Life Sciences; Cyclic GMP - analogs & derivatives; Cyclic GMP - deficiency; Cytokines; Desiccation; Disease transmission; Dosage and administration; Drying; Female; Food consumption; Food contamination; Food production; Foodborne diseases; Health care costs; Hogs; Immune response; Immune system; Immunogenicity; Immunology; Immunotherapy; Impact analysis; Infections; Innate immunity; Interferon; Interferon-gamma - blood; Interleukin 10; Interleukin 17; Interleukin 2; Interleukin-10 - blood; Interleukin-17 - blood; Interleukin-2 - blood; Laboratories; Medical research; Medicine and Health Sciences; Messenger RNA; Mice; Mice, Inbred BALB C; Mutation; Oral vaccines; Pathogens; Pneumoviridae; Prevention; Proteins; Research and Analysis Methods; Risk factors; Salmonella; Salmonella enterica; Salmonella Infections, Animal - immunology; Salmonella Infections, Animal - prevention & control; Salmonella typhimurium; Salmonella typhimurium - immunology; Salmonella Vaccines - administration & dosage; Salmonella Vaccines - immunology; Salmonella Vaccines - therapeutic use; Salmonellosis; Sigma Factor - physiology; Statistics; Tumor Necrosis Factor-alpha - blood; Tumor necrosis factor-α; Vaccination; Vaccines; Vaccines, Attenuated - administration & dosage; Vaccines, Attenuated - immunology; Vaccines, Attenuated - therapeutic use; Virulence; Virulence factors; Zoonoses; γ-Interferon
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0161216

Salmonellosis is one of the most important bacterial zoonotic diseases transmitted through the consumption of contaminated food, with chicken and pig related products being key reservoirs of infection. Although numerous studies on animal vaccination have been performed in order to reduce Salmonella prevalence, there is still a need for an ideal vaccine. Here, with the aim of constructing a novel live attenuated Salmonella vaccine candidate, we firstly analyzed the impact of the absence of cyclic-di-GMP (c-di-GMP) in Salmonella virulence. C-di-GMP is an intracellular second messenger that controls a wide range of bacterial processes, including biofilm formation and synthesis of virulence factors, and also modulates the host innate immune response. Our results showed that a Salmonella multiple mutant in the twelve genes encoding diguanylate cyclase proteins that, as a consequence, cannot synthesize c-di-GMP, presents a moderate attenuation in a systemic murine infection model. An additional mutation of the rpoS gene resulted in a synergic attenuating effect that led to a highly attenuated strain, referred to as ΔXIII, immunogenic enough to protect mice against a lethal oral challenge of a S. Typhimurium virulent strain. ΔXIII immunogenicity relied on activation of both antibody and cell mediated immune responses characterized by the production of opsonizing antibodies and the induction of significant levels of IFN-γ, TNF-α, IL-2, IL-17 and IL-10. ΔXIII was unable to form a biofilm and did not survive under desiccation conditions, indicating that it could be easily eliminated from the environment. Moreover, ΔXIII shows DIVA features that allow differentiation of infected and vaccinated animals. Altogether, these results show ΔXIII as a safe and effective live DIVA vaccine.