Background Burkholderia pseudomallei is the causative agent of melioidosis, a disease of significant morbidity and mortality in both human and animals in endemic areas. There is no vaccine towards the bacterium available in the market, and the efficacy of many of the bacterium's surface and secreted proteins are currently being evaluated as vaccine candidates.Methodology/Principal FindingsWith the availability of the B. pseudomallei whole genome sequence, we undertook to identify genes encoding the known immunogenic outer membrane protein A (OmpA). Twelve OmpA domains were identified and ORFs containing these domains were fully annotated. Of the 12 ORFs, two of these OmpAs, Omp3 and Omp7, were successfully cloned, expressed as soluble protein and purified. Both proteins were recognised by antibodies in melioidosis patients' sera by Western blot analysis. Purified soluble fractions of Omp3 and Omp7 were assessed for their ability to protect BALB/c mice against B. pseudomallei infection. Mice were immunised with either Omp3 or Omp7, subsequently challenged with 1×106 colony forming units (cfu) of B. pseudomallei via the intraperitoneal route, and examined daily for 21 days post-challenge. This pilot study has demonstrated that whilst all control unimmunised mice died by day 9 post-challenge, two mice (out of 4) from both immunised groups survived beyond 21 days post-infection.Conclusions/SignificanceWe have demonstrated that B. pseudomallei OmpA proteins are immunogenic in mice as well as melioidosis patients and should be further assessed as potential vaccine candidates against B. pseudomallei infection.

BackgroundChronic bacterial infections occur as a result of the infecting pathogen’s ability to live within a biofilm, hence escaping the detrimental effects of antibiotics and the immune defense system. Burkholderia pseudomallei, a gram-negative facultative pathogen, is distinctive in its ability to survive within phagocytic and non-phagocytic cells, to persist in vivo for many years and subsequently leading to relapse as well as the development of chronic disease. The capacity to persist has been attributed to the pathogen’s ability to form biofilm. However, the underlying biology of B. pseudomallei biofilm development remains unresolved.ResultsWe utilised RNA-Sequencing to identify genes that contribute to B. pseudomallei biofilm phenotype. Transcriptome analysis of a high and low biofilm producer identified 563 differentially regulated genes, implying that expression of ~9.5 % of the total B. pseudomallei gene content was altered during biofilm formation. Genes involved in surface-associated motility, surface composition and cell wall biogenesis were over-expressed and probably play a role in the initial attachment of biofilms. Up-regulation of genes related to two component signal transduction systems and a denitrification enzyme pathway suggest that the B. pseudomallei high biofilm producer is able to sense the surrounding environmental conditions and regulate the production of extracellular polymeric substance matrix, a hallmark of microbial biofilm formation.ConclusionsThe transcriptome profile described here provides the first comprehensive view of genes that contribute to the biofilm phenotype in B. pseudomallei.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1692-0) contains supplementary material, which is available to authorized users.

BackgroundBurkholderia pseudomallei, the causative agent of melioidosis, is endemic to Southeast Asia and northern Australia. Clinical manifestations of disease are diverse, ranging from chronic infection to acute septicaemia. The current gold standard of diagnosis involves bacterial culture and identification which is time consuming and often too late for early medical intervention. Hence, rapid diagnosis of melioidosis is crucial for the successful management of melioidosis.MethodsThe study evaluated 4 purified B. pseudomallei recombinant proteins (TssD-5, Omp3, smBpF4 and Omp85) as potential diagnostic agents for melioidosis. A total of 68 sera samples from Malaysian melioidosis patients were screened for the presence of specific antibodies towards these proteins using enzyme-linked immunosorbent assay (ELISA). Sera from patients with various bacterial and viral infections but negative for B. pseudomallei, as well as sera from healthy individuals, were also included as non-melioidosis controls. The Mann Whitney test was performed to compare the statistical differences between melioidosis patients and the non-melioidosis controls.ResultsTssD-5 demonstrated the highest sensitivity of 71% followed by Omp3 (59%), smBpF4 (41%) and Omp85 (19%). All 4 antigens showed equally high specificity (89-96%). A cocktail of all 4 antigens resulted in slightly reduced sensitivity of 65% but improved specificity (99%). Multiple-antigen ELISA provided improved sensitivity of 88.2% whilst retaining good specificity (96%). There was minimal reactivity with sera from healthy individuals proposing the utility of these antigens to demarcate diseased from non-symptomatic individuals in an endemic country.ConclusionsTssD-5 demonstrated high detection sensitivity and specificity and the results were obtained within a few hours compared to time consuming culture and IFAT methods commonly used in a clinical setting. The use of multiple-antigens resulted in improved sensitivity (88.2%) whilst maintaining superior specificity. These data highlight the use of TssD-5 and other recombinant antigens tested in this study as potential serodiagnostic agents for melioidosis.