Improvement of recombinant-truncated Burkholderia motility protein A (BimA)-based indirect ELISA for equine glanders.

Glanders is a contagious and highly fatal disease of equines with zoonotic potential. It is caused by a Gram-negative, nonmotile bacterium Burkholderia mallei. Complement fixation test (CFT) is one of the most commonly used tests for diagnosis of glanders; however, it has some limitations. A recombinant-truncated Burkholderia intracellular motility A (BimA) protein-based indirect enzyme-linked immunosorbent assay (iELISA) was previously reported by us for glanders diagnosis, which has been re-optimized in this study using a panel of glanders positive (n = 75) and glanders negative (n = 227) serum samples. The improved iELISA exhibited 96% sensitivity and 90.75% specificity. The assay had 98.56% negative predictive value. In the improved iELISA, background for negative samples was reduced and a rational assay cut-off based on ROC curves was introduced. Intra laboratory repeatability of the iELISA was tested by 3 different operators with 100% correlation. The BimA-coated ELISA plates could be used without significant decrease in diagnostic efficacy even after their storage at room temperature or 37°C for 90 days. Overall, the improved iELISA is a sensitive, specific, reproducible, and easy-to-use assay that has potential in serodiagnosis of glanders, more suitably to demonstrate freedom from B. mallei infection in a population.

Identification of a new diagnostic antigen for glanders using immunoproteome analysis.

Glanders is a disease of horses, donkeys and mules. The causative agent Burkholderia mallei, is a biorisk group 3 pathogen and is also a biothreat agent. Simple and rapid diagnostic tool is essential for control of glanders. Using a proteomic approach and immunoblotting with equine sera, we identified 12 protein antigens that may have diagnostic potential. Various immunoreactive proteins e.g. GroEL, translation elongation factor Tu, elongation factor Ts, arginine deiminase, malate dehydrogenase, DNA directed RNA polymerase subunit alpha were identified on 2-dimentional immunoblots. One of these proteins, GroEL, was cloned and expressed in E. coli and purified using Ni-NTA affinity chromatography. The recombinant GroEL protein was evaluated in ELISA format on a panel of glanders positive (n=49) and negative (n=79) equine serum samples to determine its diagnostic potential. The developed ELISA had a sensitivity and specificity of 96 and 98.7% respectively. The results of this study highlight the potential of GroEL in serodiagnosis of glanders.

Prediction of T cell epitopes of Brucella abortus and evaluation of their protective role in mice.

Brucellae are Gram-negative intracellular bacteria that cause an important zoonotic disease called brucellosis. The animal vaccines are available but have disadvantage of causing abortions in a proportion of pregnant animals. The animal vaccines are also pathogenic to humans. Recent trend in vaccine design has shifted to epitope-based vaccines that are safe and specific. In this study, efforts were made to identify MHC-I- and MHC-II-restricted T cell epitopes of Brucella abortus and evaluate their vaccine potential in mice. The peptides were designed using online available immunoinformatics tools, and five MHC-I- and one MHC-II-restricted T cell peptides were selected on the basis of their ability to produce interferon gamma (IFN-γ) in in vivo studies. The selected peptides were co-administered with poly DL-lactide-co-glycolide (PLG) microparticles and evaluated for immunogenicity and protection in BALB/c mice. Mice immunized with peptides either entrapped in PLG microparticles (EPLG-Pep) or adsorbed on PLG particles (APLG-Pep) showed significantly higher splenocyte proliferation and IFN-γ generation to all selected peptides than the mice immunized with corresponding irrelevant peptides formulated PLG microparticles or phosphate-buffered saline (PBS). A significant protection compared to PBS control was also observed in EPLG-Pep and APLG-Pep groups. A plasmid DNA vaccine construct (pVaxPep) for peptides encoding DNA sequences was generated and injected to mice by in vivo electroporation. Significant protection was observed (1.66 protection units) when compared with PBS and empty vector control group animals. Overall, the MHC-I and MHC-II peptides identified in this study are immunogenic and protective in mouse model and support the feasibility of peptide-based vaccine for brucellosis.

Evaluation of immunogenicity and protective efficacy of a plasmid DNA vaccine encoding ribosomal protein L9 of Brucella abortus in BALB/c mice.

Brucellosis is a worldwide zoonotic disease. No Brucella vaccine is available for use in humans and existing animal vaccines have limitations. We have previously described the ribosomal protein L9 to have the vaccine potential. In this study, L9 based DNA vaccine (pVaxL9) was generated and evaluated in mouse model. Intramuscular immunisation of pVaxL9 was able to elicit the anti-L9 IgG antibody response of both IgG1 and IgG2a isotypes when compared with PBS and pVax immunised control animals. Heightened antibody response was observed in mice groups immunised with pVaxL9 priming and recombinant L9 boosting (PB) and where pDNA immunisation was carried out by in vivo electroporation (EP). The vaccine groups proliferated splenocytes and released Th1 type cytokines e.g. IFN-γ, TNF-α, IL-2. Further, flow cytometric analysis revealed that IFN-γ was released by both by CD4+ and CD8+ T cells particularly in PB and EP groups when compared with mice immunised with empty control vector. The L9 based pDNA vaccine was able to confer significant protection in mice against challenge with virulent B. abortus with PB and EP groups offering better protection. Taken together, it can be concluded that L9 based DNA vaccine is immunogenic and confer protection in mouse model.