Protective efficacy of a canine brucellosis vaccine candidate based on live attenuated Salmonella expressing recombinant Brucella BCSP31, Omp3b and SOD proteins in Beagles

Abstract

The aim of this study was to establish a proof-of-concept of protective efficacy of Salmonella-based B. abortus vaccine candidate in Beagles. Group A Beagles (n=10) were subcutaneously (SC) inoculated with S. Typhimurium delivery strain containing pMMP65 (vector to deliver antigens) only as vector control. Group B Beagles (n=10) were SC vaccinated with the mixture of the three Salmonella delivery strains expressing the recombinant B. abortus BCSP31, Outer membrane protein 3b (Omp3b), and superoxide dismutase (SOD) proteins, respectively. No Salmonella delivery strains were isolated from all tissues tested. Serum IgG, interleukin-4, tumor necrosis factor-alpha, and interferon-gamma concentrations were significantly higher in group B than in group A. Following intraconjunctival challenge with B. abortus 544, among 5 group B Beagles, the challenge strain was isolated from mandibular, and retropharyngeal lymph nodes of three Beagles, and no isolates were observed from all tissues of two Beagle. However, the challenge strains were detected from spleen, uterus (except two Beagles), and mandibular, prescapular, retropharyngeal, and superficial inguinal lymph nodes of all group A Beagles. These results suggest that the mixture of three S. Typhimurium delivery strains be a good vaccine candidate against brucellosis by B. abortus in dogs. Further investigations are needed to improve the protective efficacy of the Salmonella-based B. abortus vaccine candidate and explore its practical application in dogs.

Keywords: Brucella abortus; S. Typhimurium-based B. abortus vaccine; attenuated Salmonella Typhimurium; dog; immunization.

Fig. 1.

Antibody titers (optical density) against each recombinant BCSP31, Omp3b, and SOD protein. Group A Beagles were inoculated with attenuated Salmonella Typhimurium containing pMMP65 only as a vector control. Group B Beagles were immunized with approximately 3.0 × 10⁹ CFU/ml of the mixture of S. Typhimurium delivery strains expressing recombinant BCSP31, Omp3b, and SOD proteins in 1 ml. Data represent the means of all Beagles in each group, and error bars represent the standard deviations (SDs). Asterisks indicate a significant difference between the values obtained for the immunized group and those obtained for the vector control group (*P<0.05).

Fig. 2.

IL-4, TNF-α, and IFN-γ concentrations (pg/ml) in peripheral blood mononuclear cells at 6 weeks post prime immunization. Groups A, and B are indicated as in Fig. 1. Data represent the means of all Beagles in each group, and error bars indicate the standard deviations (SDs). Asterisks indicate significant differences among the values obtained for each group (*P<0.05).

Fig. 3.

Index of infection for Beagles challenged with B. abortus strain 544 at 6 weeks post prime immunization (A), colonization and incidence of recovery of B. abortus strain 544 in tissues (B). Groups A, and B are indicated as in Fig. 1. All Beagles in each group were conjunctivaly challenged with approximately 2 × 10⁷ CFU of virulent B. abortus 544 at 6 weeks post prime immunization. The numbers of viable bacteria recovered from each tissues of Beagles at 8 weeks post challenge are shown. LN, lymph node.