Burkholderia Hep_Hag autotransporter (BuHA) proteins elicit a strong antibody response during experimental glanders but not human melioidosis

Background The bacterial biothreat agents Burkholderia mallei and Burkholderia pseudomallei are the cause of glanders and melioidosis, respectively. Genomic and epidemiological studies have shown that B. mallei is a recently emerged, host restricted clone of B. pseudomallei. Results Using bacteriophage-mediated immunoscreening we identified genes expressed in vivo during experimental equine glanders infection. A family of immunodominant antigens were identified that share protein domain architectures with hemagglutinins and invasins. These have been designated Burkholderia Hep_Hag autotransporter (BuHA) proteins. A total of 110/207 positive clones (53%) of a B. mallei expression library screened with sera from two infected horses belonged to this family. This contrasted with 6/189 positive clones (3%) of a B. pseudomallei expression library screened with serum from 21 patients with culture-proven melioidosis. Conclusion Members of the BuHA proteins are found in other Gram-negative bacteria and have been shown to have important roles related to virulence. Compared with other bacterial species, the genomes of both B. mallei and B. pseudomallei contain a relative abundance of this family of proteins. The domain structures of these proteins suggest that they function as multimeric surface proteins that modulate interactions of the cell with the host and environment. Their effect on the cellular immune response to B. mallei and their potential as diagnostics for glanders requires further study

An international, multicentre evaluation and description of Burkholderia pseudomallei infection in cystic fibrosis

BACKGROUND: Several cases of Burkholderia pseudomallei infection in CF have been previously reported. We aimed to identify all cases globally, risk factors for acquisition, clinical consequences, and optimal treatment strategies. METHODS: We performed a literature search to identify all published cases of B. pseudomallei infection in CF. In addition we hand-searched respiratory journals, and contacted experts in infectious diseases and CF around the world. Supervising clinicians for identified cases were contacted and contemporaneous clinical data was requested. RESULTS: 25 culture-confirmed cases were identified. The median age at acquisition was 21 years, mean FEV(1) % predicted was 60 %, and mean BMI was 19.5 kg/m(2). The location of acquisition was northern Australia or south-east Asia for most. 19 patients (76 %) developed chronic infection, which was usually associated with clinical decline. Successful eradication strategies included a minimum of two weeks of intravenous ceftazidime, followed by a consolidation phase with trimethoprim/sulfamethoxazole, and this resulted in a higher chance of success when instituted early. Three cases of lung transplantation have been recorded in the setting of chronic B. pseudomallei infection. CONCLUSION: Chronic carriage of B. pseudomallei in patients with CF appears common after infection, in contrast to the non-CF population. This is often associated with an accelerated clinical decline. Lung transplantation has been performed in select cases of chronic B. pseudomallei infection. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12890-015-0109-9) contains supplementary material, which is available to authorized users

Structure analysis of biologically important prokaryotic glycopolymers

Of the many post-translational modifications organisms can undertake, glycosylation is the most prevalent and the most diverse. The research in this thesis focuses on the structural characterisation of glycosylation in two classes of glycopolymer (lipopolysaccharide (LPS) and glycoprotein) in two domains of life (bacteria and archaea). The common theme linking these subprojects is the development and application of high sensitivity analytical techniques, primarily mass spectrometry (MS), for studying prokaryotic glycosylation. Many prokaryotes produce glycan arrangements with extraordinary variety in composition and structure. A further challenge is posed by additional functionalities such as lipids whose characterisation is not always straightforward. Glycosylation in prokaryotes has a variety of different biological functions, including their important roles in the mediation of interactions between pathogens and hosts. Thus enhanced knowledge of bacterial glycosylation may be of therapeutic value, whilst a better understanding of archaeal protein glycosylation will provide further targets for industrial applications, as well as insight into this post- translational modification across evolution and protein processing under extreme conditions. The first sub-project focused on the S-layer glycoprotein of the halophilic archeaon Haloferax volcanii, which has been reported to be modified by both glycans and lipids. Glycoproteomic and associated MS technologies were employed to characterise the N- and O-linked glycosylation and to explore putative lipid modifications. Approximately 90% of the S-layer was mapped and N-glycans were identified at all the mapped consensus sites, decorated with a pentasaccharide consisting of two hexoses, two hexuronic acids and a methylated hexuronic acid. The O-glycans are homogeneously identified as a disaccharide consisting of galactose and glucose. Unexpectedly it was found that membrane-derived lipids were present in the S- layer samples despite extensive purification, calling into question the predicted presence of covalently linked lipid. The H. volcanii N-glycosylation is mediated by the products of the agl gene cluster and the functional characterisation of members of the agl gene cluster was investigated by MS analysis of agl-mutant strains of the S-layer. Burkholderia pseudomallei is the causative agent of melioidosis, a serious and often fatal disease in humans which is endemic in South-East Asia and other equatorial regions. Its LPS is vital for serum resistance and the O-antigen repeat structures are of interest as vaccine targets. B. pseudomallei is reported to produce several polysaccharides, amongst which the already characterised ‘typical’ O-antigen of K96243 represents 97% of the strains. The serologically distinct ‘atypical’ strain 576 produces a different LPS, whose characterisation is the subject of this research project. MS strategies coupled with various hydrolytic and chemical derivatisation methodologies were employed to define the composition and potential sequences of the O-antigen repeat unit. These MS strategies were complemented by a novel NMR technique involving embedding of the LPS into micelles. Taken together the MS and NMR data have revealed a highly unusual O-antigen structure for atypical LPS which is remarkably different from the typical O-antigen. The development of structural analysis tools in MS and NMR applicable to the illustrated types of glycosylation in these prokaryotes will give a more consistent approach to sugar characterisation and their modifications thus providing more informative results for pathogenicity and immunological studies as well as pathway comparisons.Open Acces

A Machine Learning-Based Raman Spectroscopic Assay for the Identification of Burkholderia mallei and Related Species

Burkholderia (B.) mallei, the causative agent of glanders, and B. pseudomallei, the causative agent of melioidosis in humans and animals, are genetically closely related. The high infectious potential of both organisms, their serological cross-reactivity, and similar clinical symptoms in human and animals make the differentiation from each other and other Burkholderia species challenging. The increased resistance against many antibiotics implies the need for fast and robust identification methods. The use of Raman microspectroscopy in microbial diagnostic has the potential for rapid and reliable identification. Single bacterial cells are directly probed and a broad range of phenotypic information is recorded, which is subsequently analyzed by machine learning methods. Burkholderia were handled under biosafety level 1 (BSL 1) conditions after heat inactivation. The clusters of the spectral phenotypes and the diagnostic relevance of the Burkholderia spp. were considered for an advanced hierarchical machine learning approach. The strain panel for training involved 12 B. mallei, 13 B. pseudomallei and 11 other Burkholderia spp. type strains. The combination of top- and sub-level classifier identified the mallei-complex with high sensitivities (>95%). The reliable identification of unknown B. mallei and B. pseudomallei strains highlighted the robustness of the machine learning-based Raman spectroscopic assay

Type three secretion system-mediated escape of Burkholderia pseudomallei into the host cytosol is critical for the activation of NFκB.

BackgroundBurkholderia pseudomallei is the causative agent of melioidosis, a potentially fatal disease endemic in Southeast Asia and Northern Australia. This Gram-negative pathogen possesses numerous virulence factors including three "injection type" type three secretion systems (T3SSs). B. pseudomallei has been shown to activate NFκB in HEK293T cells in a Toll-like receptor and MyD88 independent manner that requires T3SS gene cluster 3 (T3SS3 or T3SSBsa). However, the mechanism of how T3SS3 contributes to NFκB activation is unknown.ResultsKnown T3SS3 effectors are not responsible for NFκB activation. Furthermore, T3SS3-null mutants are able to activate NFκB almost to the same extent as wildtype bacteria at late time points of infection, corresponding to delayed escape into the cytosol. NFκB activation also occurs when bacteria are delivered directly into the cytosol by photothermal nanoblade injection.ConclusionsT3SS3 does not directly activate NFκB but facilitates bacterial escape into the cytosol where the host is able to sense the presence of the pathogen through cytosolic sensors leading to NFκB activation

Genome-wide saturation mutagenesis of Burkholderia pseudomallei K96243 predicts essential genes and novel targets for antimicrobial development.

UNLABELLED: Burkholderia pseudomallei is the causative agent of melioidosis, an often fatal infectious disease for which there is no vaccine. B. pseudomallei is listed as a tier 1 select agent, and as current therapeutic options are limited due to its natural resistance to most antibiotics, the development of new antimicrobial therapies is imperative. To identify drug targets and better understand the complex B. pseudomallei genome, we sought a genome-wide approach to identify lethal gene targets. As B. pseudomallei has an unusually large genome spread over two chromosomes, an extensive screen was required to achieve a comprehensive analysis. Here we describe transposon-directed insertion site sequencing (TraDIS) of a library of over 10(6) transposon insertion mutants, which provides the level of genome saturation required to identify essential genes. Using this technique, we have identified a set of 505 genes that are predicted to be essential in B. pseudomallei K96243. To validate our screen, three genes predicted to be essential, pyrH, accA, and sodB, and a gene predicted to be nonessential, bpss0370, were independently investigated through the generation of conditional mutants. The conditional mutants confirmed the TraDIS predictions, showing that we have generated a list of genes predicted to be essential and demonstrating that this technique can be used to analyze complex genomes and thus be more widely applied. IMPORTANCE: Burkholderia pseudomallei is a lethal human pathogen that is considered a potential bioterrorism threat and has limited treatment options due to an unusually high natural resistance to most antibiotics. We have identified a set of genes that are required for bacterial growth and thus are excellent candidates against which to develop potential novel antibiotics. To validate our approach, we constructed four mutants in which gene expression can be turned on and off conditionally to confirm that these genes are required for the bacteria to survive

Identification and characterisation of toxin-antitoxin systems (TA) in Burkholderia pseudomallei

The aim of this study was to identify and characterise type II toxin-antitoxin (TA) systems in Burkholderia pseudomallei, the causative agent of the human disease melioidosis. 8 putative TA systems were identified within the genome of B. pseudomallei K96243. 5 of these were located witihn genome islands. Of the candidate toxins, BPSL0175 (RelE1) or BPSS1060 (RelE2) caused growth to cease when expressed in Escherichia coli, whereas expression of BPSS0390 (HicA) or BPSS1584 (HipA) (in an E. coli ΔhipBA background) caused a reduction in the number of culturable bacteria. HicA also caused growth arrest in B. pseudomallei K96243 ΔhicAB. These toxin induced phenotypes were enhanced by an <3kDa extracellular factor that accumulated in the spent medium during growth. Expression of the cognate antitoxins could restore growth and culturability of cells. Expression of hicA in E. coli gave an increased number of persister cells in response to ciprofloxacin or ceftazidime. Site directed mutagenesis studies identified two key residues within the HicA toxin that were essential for both the reduced culturability and increased persistence phenotypes. Deletion of hicAB from B. pseudomallei K96243 did not affect persister cell or survival frequencies compared to the wild type following treatment with a variety of stress conditions. Deletion of the ΔhipBA locus from B. pseudomallei K96243 also had no affect on bacterial persistence or survival under the conditions tested

Melioidosis in the Philippines.

The first documented case of melioidosis in the Philippines occurred in 1948. Since then, there have been sporadic reports in the literature about travelers diagnosed with melioidosis after returning from the Philippines. Indigenous cases, however, have been documented rarely, and under-reporting is highly likely. This review collated all Philippine cases of melioidosis published internationally and locally, as well as unpublished case series and reports from different tertiary hospitals in the Philippines. In total, 25 papers and 41 cases were identified. Among these, 23 were indigenous cases (of which 20 have not been previously reported in the literature). The most common co-morbidity present was diabetes mellitus, and the most common presentations were pulmonary and soft tissue infections. Most of the cases received ceftazidime during the intensive phase, while trimethoprim-sulfamethoxazole was given during the eradication phase. The known mortality rate was 14.6%, while 4.9% of all cases were reported to have had recurrence. The true burden of melioidosis in the country is not well defined. A lack of awareness among clinicians, a dearth of adequate laboratories, and the absence of a surveillance system for the disease are major challenges in determining the magnitude of the problem