Protective antigens against glanders identified by expression library immunization

Burkholderia are highly evolved Gram-negative bacteria that primarily infect solipeds but are transmitted to humans by ingestion and cutaneous or aerosol exposures. Heightened concern over human infections of Burkholderia mallei and the very closely related species B. pseudomallei is due to the pathogens' proven effectiveness as bioweapons, and to the increased potential for natural opportunistic infections in the growing diabetic and immuno-compromised populations. These Burkholderia species are nearly impervious to antibiotic treatments and no vaccine exists. In this study, the genome of the highly virulent B. mallei ATCC23344 strain was examined by expression library immunization for gene-encoded protective antigens. This protocol for genomic-scale functional screening was customized to accommodate the unusually large complexity of Burkholderia, and yielded 12 new putative vaccine candidates. Five of the candidates were individually tested as protein immunogens and three were found to confer significant partial protection against a lethal pulmonary infection in a murine model of disease. Determinations of peripheral blood cytokine and chemokine profiles following individual protein immunizations show that interleukin-2 (IL-2) and IL-4 are elicited by the three confirmed candidates, but unexpectedly interferon-γ and tumor necrosis factor-α are not. We suggest that these pathogen components, discovered using genetic immunization and confirmed in a conventional protein format, will be useful toward the development of a safe and effective glanders vaccine.

Development of reagents and assays for the detection of pathogenic Burkholderia species

Rapid detection of the category B biothreat agents Burkholderia pseudomallei and Burkholderia mallei in acute infections is critical to ensure that appropriate treatment is administered quickly to reduce an otherwise high probability of mortality (ca. 40% for B. pseudomallei). We are developing assays that can be used in clinical laboratories or security applications for the direct detection of surface-localized and secreted macromolecules produced by these organisms. We present our current medium-throughout approach for target selection and production of Burkholderia macromolecules and describe the generation of a Fab molecule targeted to the B. mallei BimA protein. We also present development of prototype assays for detecting Burkholderia species using anti-lipopolysaccharide antibodies.

Protective response to subunit vaccination against intranasal Burkholderia mallei and B. pseudomallei challenge

Burkholderia mallei and B. pseudomallei are Gram-negative pathogenic bacteria, responsible for the diseases glanders and melioidosis, respectively. Furthermore, there is currently no vaccine available against these Burkholderia species. In this study, we aimed to identify protective proteins against these pathogens. Immunization with recombinant B. mallei Hcp1 (type VI secreted/structural protein), BimA (autotransporter protein), BopA (type III secreted protein), and B. pseudomallei LolC (ABC transporter protein) generated significant protection against lethal inhaled B. mallei ATCC23344 and B. pseudomallei 1026b challenge. Immunization with BopA elicited the greatest protective activity, resulting in 100% and 60% survival against B. mallei and B. pseudomallei challenge, respectively. Moreover, sera from recovered mice demonstrated reactivity with the recombinant proteins. Dendritic cells stimulated with each of the different recombinant proteins showed distinct cytokine patterns. In addition, T cells from immunized mice produced IFN-γ following in vitro re-stimulation. These results indicated therefore that it was possible to elicit cross-protective immunity against both B. mallei and B. pseudomallei by vaccinating animals with one or more novel recombinant proteins identified in B. mallei.

Sero-characterization of lipopolysaccharide from Burkholderia thailandensis

We report the successful purification of lipopolysaccharide (LPS) from Burkholderia thailandensis, a Gram-negative bacterium, closely related to the highly pathogenic organisms B. pseudomallei and B. mallei. Burkholderia thailandensis LPS is shown to cross-react with rabbit and mouse sera obtained from inoculation with B. pseudomallei or B. mallei, respectively. These data suggest that B. thailandensis LPS shares similar structural features with LPS molecules from highly pathogenic Burkholderia species. This information may prove useful in ongoing efforts to develop novel vaccines and/or diagnostic reagents.

Burkholderia mallei cellular interactions in a respiratory cell model

Burkholderia mallei is a facultative intracellular pathogen that survives and replicates in phagocytic cell lines. The bacterial burden recovered from naïve BALB/c mice infected by intranasal delivery indicated that B. mallei persists in the lower respiratory system. To address whether B. mallei invades respiratory non-professional phagocytes, this study utilized A549 and LA-4 respiratory epithelial cells and demonstrated that B. mallei possesses the capacity to adhere poorly to, but not to invade, these cells. Furthermore, it was found that B. mallei was taken up by the murine alveolar macrophage cell line MH-S following serum coating, an attribute suggestive of complement- or Fc receptor-mediated uptake. Invasion/intracellular survival assays of B. mallei-infected MH-S cells demonstrated decreased intracellular survival, whilst a type III secretion system effector bopA mutant strain survived longer than the wild-type. Evaluation of the potential mechanism(s) responsible for efficient clearing of intracellular organisms demonstrated comparable levels of caspase-3 in both the wild-type and bopA mutant with characteristics consistent with apoptosis of infected MH-S cells. Furthermore, challenge of BALB/c mice with the bopA mutant by the intranasal route resulted in increased survival. Overall, these data suggest that B. mallei induces apoptotic cell death, whilst the BopA effector protein participates in intracellular survival.

High-throughput multistrain polymerase chain reaction quantification of Chlamydia trachomatis from clinical and preclinical urogenital specimens

Chlamydia trachomatis (CT) is the most prevalent sexually transmitted bacterial pathogen worldwide and causes severe reproductive tract infections. Currently, nucleic acid amplification tests (NAATs) are the gold standard for clinical diagnosis, but most NAATs are labor intensive and limited to specific CT serovars. We developed and validated a quantitative polymerase chain reaction (qPCR) assay that reproducibly detected CT serovars D, E, F, Ia, and Chlamydia muridarum over a linear range of 2 log(10) to 10 log(10) genomes with low coefficients of variation from both experimental and human urine samples. CT DNA loads from human vaginal, endocervical, and male urethral swabs correlated well with the BD ProbeTec ET assay (Becton Dickinson Diagnostic Systems, Franklin Lakes, NJ) run in parallel. In a preclinical microbicide evaluation, C. muridarum DNA loads in mouse swabs and tissues correlated well with an immunofluorescence assay. The optimized qPCR system provided enhanced sensitivity and facilitated the quantitative evaluation of clinical and experimental preclinical samples for anti-CT therapeutic and microbicide evaluation.

Development of a non-living vaccine against Burkholderia mallei (129.2)

Burkholderia mallei is a gram-negative highly pathogenic bacterium, responsible for glanders. B. mallei is considered potential bioterrorism agents, classified as such in list B by the Centers for Disease Control and Prevention. Currently there is no vaccine available against B. mallei. In this study, we aimed to identify the protective proteins of B. mallei. The candidate proteins were selected based on the previous data of proteomics and linear expression library (LEE) whole-genome screens coupled with known structures or functions of the proteins in other bacteria. The selected proteins were BMA-4, BMA-8, BMA-9, BMA-10, BMA-11 and BMA-12. The genes encoding each protein were cloned into pCDNA3.1 and pET28a. The His-tag proteins were then purified. BALB/c mice were vaccinated with DNA encoding each protein and then boosted 3 weeks later with the recombinant proteins. Two weeks after boosting, mice were infected with B. mallei ATCC23344. The result showed that, 19 days after infection, there was 100% survival in the BMA2821 and BMAA0768 groups, however only 78% survival in the control group. The study needs to be repeated and the result will be discussed.

Host immunity in the protective response to vaccination with heat-killed Burkholderia mallei

Background

We performed initial cell, cytokine and complement depletion studies to investigate the possible role of these effectors in response to vaccination with heat-killed Burkholderia mallei in a susceptible BALB/c mouse model of infection.

Results

While protection with heat-killed bacilli did not result in sterilizing immunity, limited protection was afforded against an otherwise lethal infection and provided insight into potential host protective mechanisms. Our results demonstrated that mice depleted of either B cells, TNF-α or IFN-γ exhibited decreased survival rates, indicating a role for these effectors in obtaining partial protection from a lethal challenge by the intraperitoneal route. Additionally, complement depletion had no effect on immunoglobulin production when compared to non-complement depleted controls infected intranasally.

Conclusion

The data provide a basis for future studies of protection via vaccination using either subunit or whole-organism vaccine preparations from lethal infection in the experimental BALB/c mouse model. The results of this study demonstrate participation of B220⁺ cells and pro-inflammatory cytokines IFN-γ and TNF-α in protection following HK vaccination.

Glanders: off to the races with Burkholderia mallei

Burkholderia mallei, the etiologic agent of the disease known as glanders, is primarily a disease affecting horses and is transmitted to humans by direct contact with infected animals. The use of B. mallei as a biological weapon has been reported and currently, there is no vaccine available for either humans or animals. Despite the history and highly infective nature of B. mallei, as well as its potential use as a bio-weapon, B. mallei research to understand the pathogenesis and the host responses to infection remains limited. Therefore, this minireview will focus on current efforts to elucidate B. mallei virulence, the associated host immune responses elicited during infection and discuss the feasibility of vaccine development.