Characterization of the capsular polysaccharide of Burkholderia (Pseudomonas) pseudomallei 304b

β-Stereoselective Kdo C-glycosylation by a (p-Tol)2SO/Tf2O preactivation strategy

There is very little research on the synthesis of β-3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) C-glycosides, which restricted their widespread application. Herein, a convenient and efficient approach to synthesize β-Kdo C-glycosides was developed based on a Tf2O/(p-Tol)2SO preactivation strategy using bench stable peracetylated Kdo thioglycoside as a donor via a thermodynamic SN1-like mechanism.

The Arabinose 5-Phosphate Isomerase KdsD Is Required for Virulence in Burkholderia pseudomallei

Burkholderia pseudomallei is the causative agent of melioidosis, which is endemic primarily in Southeast Asia and northern Australia but is increasingly being seen in other tropical and subtropical regions of the world. Melioidosis is associated with high morbidity and mortality rates, which is mediated by the wide range of virulence factors encoded by B. pseudomallei. These virulence determinants include surface polysaccharides such as lipopolysaccharide (LPS) and capsular polysaccharides (CPS). Here, we investigated a predicted arabinose-5-phosphate isomerase (API) similar to KdsD in B. pseudomallei strain K96243. KdsD is required for the production of the highly conserved 3-deoxy-d-manno-octulosonic acid (Kdo), a key sugar in the core region of LPS. Recombinant KdsD was expressed and purified, and API activity was determined. Although a putative API paralogue (KpsF) is also predicted to be encoded, the deletion of kdsD resulted in growth defects, loss of motility, reduced survival in RAW 264.7 murine macrophages, and attenuation in a BALB/c mouse model of melioidosis. Suppressor mutations were observed during a phenotypic screen for motility, revealing single nucleotide polymorphisms or indels located in the poorly understood CPS type IV cluster. Crucially, suppressor mutations did not result in reversion of attenuation in vivo. This study demonstrates the importance of KdsD for B. pseudomallei virulence and highlights further the complex nature of the polysaccharides it produces. IMPORTANCE The intrinsic resistance of B. pseudomallei to many antibiotics complicates treatment. This opportunistic pathogen possesses a wide range of virulence factors, resulting in severe and potentially fatal disease. Virulence factors as targets for drug development offer an alternative approach to combat pathogenic bacteria. Prior to initiating early drug discovery approaches, it is important to demonstrate that disruption of the target gene will prevent the development of disease. This study highlights the fact that KdsD is crucial for virulence of B. pseudomallei in an animal model of infection and provides supportive phenotypic characterization that builds a foundation for future therapeutic development.

NHP BurkPx: A multiplex serodiagnostic bead assay to monitor Burkholderia pseudomallei exposures in non-human primates

BACKGROUND

Melioidosis is a disease caused by the bacterium Burkholderia pseudomallei, infecting humans and non-human primates (NHP) through contaminated soil or water. World-wide there are an estimated 165,000 human melioidosis cases each year, but recordings of NHP cases are sporadic. Clinical detection of melioidosis in humans is primarily by culturing B. pseudomallei, and there are no standardized detection protocols for NHP. NHP are an important animal model for melioidosis research including clinical trials and development of biodefense countermeasures.

METHODOLOGY/PRINCIPLE FINDINGS

We evaluated the diagnostic potential of the multiple antigen serological assay, BurkPx, in NHP using two sera sets: (i) 115 B. pseudomallei-challenged serum samples from 80 NHP collected each week post-exposure (n = 52) and at euthanasia (n = 47), and (ii) 126 B. pseudomallei-naïve/negative serum samples. We observed early IgM antibody responses to carbohydrate antigens followed by IgG antibody recognition to multiple B. pseudomallei protein antigens during the second week of infection. B. pseudomallei negative serum samples had low to intermediate antibody cross reactivity to the antigens in this assay. Infection time was predicted as the determining factor in the variation of antibody responses, with 77.67% of variation explained by the first component of the principal component analysis. A multiple antigen model generated a binary prediction metric ([Formula: see text]), which when applied to all data resulted in 100% specificity and 63.48% sensitivity. Removal of week 1 B. pseudomallei challenged serum samples increased the sensitivity of the model to 95%.

CONCLUSION/SIGNIFICANCE

We employed a previously standardized assay for humans, the BurkPx assay, and assessed its diagnostic potential for detection of B. pseudomallei exposure in NHP. The assay is expected to be useful for surveillance in NHP colonies, in investigations of suspected accidental releases or exposures, and for identifying vaccine correlates of protection.

Pathogenicity and virulence of Burkholderia pseudomallei

The soil saprophyte, Burkholderia pseudomallei, is the causative agent of melioidosis, a disease endemic in South East Asia and northern Australia. Exposure to B. pseudomallei by either inhalation or inoculation can lead to severe disease. B. pseudomallei rapidly shifts from an environmental organism to an aggressive intracellular pathogen capable of rapidly spreading around the body. The expression of multiple virulence factors at every stage of intracellular infection allows for rapid progression of infection. Following invasion or phagocytosis, B. pseudomallei resists host-cell killing mechanisms in the phagosome, followed by escape using the type III secretion system. Several secreted virulence factors manipulate the host cell, while bacterial cells undergo a shift in energy metabolism allowing for overwhelming intracellular replication. Polymerisation of host cell actin into “actin tails” propels B. pseudomallei to the membranes of host cells where the type VI secretion system fuses host cells into multinucleated giant cells (MNGCs) to facilitate cell-to-cell dissemination. This review describes the various mechanisms used by B. pseudomallei to survive within cells.

Polysaccharides from Burkholderia species as targets for vaccine development, immunomodulation and chemical synthesis

Covering: up to 2018 Burkholderia species are a vast group of human pathogenic, phytopathogenic, and plant- or environment-associated bacteria. B. pseudomallei, B. mallei, and B. cepacia complex are the causative agents of melioidosis, glanders, and cystic fibrosis-related infections, respectively, which are fatal diseases in humans and animals. Due to their high resistance to antibiotics, high mortality rates, and increased infectivity via the respiratory tract, B. pseudomallei and B. mallei have been listed as potential bioterrorism agents by the Centers for Disease Control and Prevention. Burkholderia species are able to produce a large network of surface-exposed polysaccharides, i.e., lipopolysaccharides, capsular polysaccharides, and exopolysaccharides, which are virulence factors, immunomodulators, major biofilm components, and protective antigens, and have crucial implications in the pathogenicity of Burkholderia-associated diseases. This review provides a comprehensive and up-to-date account regarding the structural elucidation and biological activities of surface polysaccharides produced by Burkholderia species. The chemical synthesis of oligosaccharides mimicking Burkholderia polysaccharides is described in detail. Emphasis is placed on the recent research efforts toward the development of glycoconjugate vaccines against melioidosis and glanders based on synthetic or native Burkholderia oligo/polysaccharides.

Melioidosis: molecular aspects of pathogenesis

Burkholderia pseudomallei is a gram-negative bacterium that causes melioidosis, a multifaceted disease that is highly endemic in southeast Asia and northern Australia. This facultative intracellular pathogen possesses a large genome that encodes a wide array of virulence factors that promote survival in vivo by manipulating host cell processes and disarming elements of the host immune system. Antigens and systems that play key roles in B. pseudomallei virulence include capsular polysaccharide, lipopolysaccharide, adhesins, specialized secretion systems, actin-based motility and various secreted factors. This review provides an overview of the current and steadily expanding knowledge regarding the molecular mechanisms used by this organism to survive within a host and their contribution to the pathogenesis of melioidosis.

Reliability of automated biochemical identification of Burkholderia pseudomallei is regionally dependent

Misidentifications of Burkholderia pseudomallei as Burkholderia cepacia by Vitek 2 have occurred. Multidimensional scaling ordination of biochemical profiles of 217 Malaysian and Australian B. pseudomallei isolates found clustering of misidentified B. pseudomallei isolates from Malaysian Borneo. Specificity of B. pseudomallei identification in Vitek 2 and potentially other automated identification systems is regionally dependent.

Comparative Genome Sequence Analysis Reveals the Extent of Diversity and Conservation for Glycan-Associated Proteins in Burkholderia spp

Members of the Burkholderia family occupy diverse ecological niches. In pathogenic family members, glycan-associated proteins are often linked to functions that include virulence, protein conformation maintenance, surface recognition, cell adhesion, and immune system evasion. Comparative analysis of available Burkholderia genomes has revealed a core set of 178 glycan-associated proteins shared by all Burkholderia of which 68 are homologous to known essential genes. The genome sequence comparisons revealed insights into species-specific gene acquisitions through gene transfers, identified an S-layer protein, and proposed that significantly reactive surface proteins are associated to sugar moieties as a potential means to circumvent host defense mechanisms. The comparative analysis using a curated database of search queries enabled us to gain insights into the extent of conservation and diversity, as well as the possible virulence-associated roles of glycan-associated proteins in members of the Burkholderia spp. The curated list of glycan-associated proteins used can also be directed to screen other genomes for glycan-associated homologs.

Characterization of the O-antigen in the lipopolysaccharide of Cronobacter (Enterobacter) malonaticus 3267

Cronobacter malonaticus, a Gram-negative bacterium previously known as Enterobacter sakazakii, is an opportunistic pathogen known to cause serious infection in infants and neonates. To provide aid for the serological and chemical identification of clinical, environmental, or food isolates of this emerging pathogen, the characterization of the lipopolysaccharide (LPS) O-polysaccharide (O-PS) antigens of Cronobacter spp. is being undertaken. The structural analysis of the O-PS, obtained by hydrazinolysis of the lipopolysaccharide produced by Cronobacter malonaticus HPB 3267, was investigated by composition, methylation, and two-dimensional high-resolution nuclear magnetic resonance methods, and was found to be a polymer of a branched pentasaccharide unit. This unit is composed of D-glucose (D-Glc), D-galactose (D-Gal), 2-amino-2-deoxy-D-glucose (D-GlcN), 2-amino-2-deoxy-D-galactose (D-GalN) and 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) residues (1: 1: 1: 1: 1), forms the repeating oligosaccharide in the O-PS antigen, and has the structure: [structure: see text].

The molecular and cellular basis of pathogenesis in melioidosis: how does Burkholderia pseudomallei cause disease?

Melioidosis, a febrile illness with disease states ranging from acute pneumonia or septicaemia to chronic abscesses, was first documented by Whitmore & Krishnaswami (1912). The causative agent, Burkholderia pseudomallei, was subsequently identified as a motile, gram-negative bacillus, which is principally an environmental saprophyte. Melioidosis has become an increasingly important disease in endemic areas such as northern Thailand and Australia (Currie et al., 2000). This health burden, plus the classification of B. pseudomallei as a category B biological agent (Rotz et al., 2002), has resulted in an escalation of research interest. This review focuses on the molecular and cellular basis of pathogenesis in melioidosis, with a comprehensive overview of the current knowledge on how B. pseudomallei can cause disease. The process of B. pseudomallei movement from the environmental reservoir to attachment and invasion of epithelial and macrophage cells and the subsequent intracellular survival and spread is outlined. Furthermore, the diverse assortment of virulence factors that allow B. pseudomallei to become an effective opportunistic pathogen, as well as to avoid or subvert the host immune response, is discussed. With the recent increase in genomic and molecular studies, the current understanding of the infection process of melioidosis has increased substantially, yet, much still remains to be elucidated.

Polysaccharides and virulence of Burkholderia pseudomallei

Burkholderia pseudomallei is the causative agent of melioidosis, an infectious disease of humans and animals. Gene clusters which encode capsular polysaccharide (type I O-PS) and LPS (type II O-PS), both of which play roles in virulence, have previously been identified. Here, the identification of two further putative clusters, type III O-PS and type IV O-PS, is reported. Mice challenged with type III O-PS or type IV O-PS mutants showed increased mean times to death (7.8 and 11.6 days) compared to those challenged with wild-type B. pseudomallei (3 days). To investigate the possible roles of polysaccharides in protection, mice were immunized with killed cells of wild-type B. pseudomallei or killed cells of B. pseudomallei with mutations in the O antigen, capsular polysaccharide, type III O-PS or type IV O-PS gene clusters. Immunization with all polysaccharide mutant strains resulted in delayed time to death compared to the naïve controls, following challenge with wild-type B. pseudomallei strain K96243. However, immunization with killed polysaccharide mutant strains conferred different degrees of protection, demonstrating the immunological importance of the polysaccharide clusters on the surface of B. pseudomallei.

Serodiagnosis of Burkholderia mallei infections in horses: state-of-the-art and perspectives

Burkholderia mallei causes glanders or farcy in solipeds, a disease that must be reported to the OIE (Office International des Epizooties, Paris, France). The number of reported outbreaks has increased steadily during the last decade. Serodiagnosis is hampered by the considerable number of false-positives and -negatives of the internationally prescribed tests. The major problem leading to low sensitivity and specificity of complement fixation test (CFT) and enzyme-linked immunosorbent assay (ELISA) has been linked to the test antigens currently used, i.e. crude preparations of whole cells. Future perspectives for the development and evaluation of serological test kits using well-characterized single antigens are discussed in the light of recent molecular research on B. mallei and the closely related saprozoonotic agent B. pseudomallei.

Melioidosis: epidemiology, pathophysiology, and management

Melioidosis, caused by the gram-negative saprophyte Burkholderia pseudomallei, is a disease of public health importance in southeast Asia and northern Australia that is associated with high case-fatality rates in animals and humans. It has the potential for epidemic spread to areas where it is not endemic, and sporadic case reports elsewhere in the world suggest that as-yet-unrecognized foci of infection may exist. Environmental determinants of this infection, apart from a close association with rainfall, are yet to be elucidated. The sequencing of the genome of a strain of B. pseudomallei has recently been completed and will help in the further identification of virulence factors. The presence of specific risk factors for infection, such as diabetes, suggests that functional neutrophil defects are important in the pathogenesis of melioidosis; other studies have defined virulence factors (including a type III secretion system) that allow evasion of killing mechanisms by phagocytes. There is a possible role for cell-mediated immunity, but repeated environmental exposure does not elicit protective humoral or cellular immunity. A vaccine is under development, but economic constraints may make vaccination an unrealistic option for many regions of endemicity. Disease manifestations are protean, and no inexpensive, practical, and accurate rapid diagnostic tests are commercially available; diagnosis relies on culture of the organism. Despite the introduction of ceftazidime- and carbapenem-based intravenous treatments, melioidosis is still associated with a significant mortality attributable to severe sepsis and its complications. A long course of oral eradication therapy is required to prevent relapse. Studies exploring the role of preventative measures, earlier clinical identification, and better management of severe sepsis are required to reduce the burden of this disease.

Melioidosis: epidemiology, pathophysiology, and management

Melioidosis, caused by the gram-negative saprophyte Burkholderia pseudomallei, is a disease of public health importance in southeast Asia and northern Australia that is associated with high case-fatality rates in animals and humans. It has the potential for epidemic spread to areas where it is not endemic, and sporadic case reports elsewhere in the world suggest that as-yet-unrecognized foci of infection may exist. Environmental determinants of this infection, apart from a close association with rainfall, are yet to be elucidated. The sequencing of the genome of a strain of B. pseudomallei has recently been completed and will help in the further identification of virulence factors. The presence of specific risk factors for infection, such as diabetes, suggests that functional neutrophil defects are important in the pathogenesis of melioidosis; other studies have defined virulence factors (including a type III secretion system) that allow evasion of killing mechanisms by phagocytes. There is a possible role for cell-mediated immunity, but repeated environmental exposure does not elicit protective humoral or cellular immunity. A vaccine is under development, but economic constraints may make vaccination an unrealistic option for many regions of endemicity. Disease manifestations are protean, and no inexpensive, practical, and accurate rapid diagnostic tests are commercially available; diagnosis relies on culture of the organism. Despite the introduction of ceftazidime- and carbapenem-based intravenous treatments, melioidosis is still associated with a significant mortality attributable to severe sepsis and its complications. A long course of oral eradication therapy is required to prevent relapse. Studies exploring the role of preventative measures, earlier clinical identification, and better management of severe sepsis are required to reduce the burden of this disease.

Exopolysaccharides produced by Burkholderia cenocepacia recA lineages IIIA and IIIB

Clinical and environmental strains of Burkholderia cenocepacia belonging to the recA lineages IIIA and IIIB were examined for exopolysaccharide (EPS) production. The exopolysaccharides structure was determined using mainly gas chromatography coupled to mass spectrometry and NMR spectroscopy. All the strains produced Cepacian, a highly branched polysaccharide constituted of a heptasaccharide repeating unit, composed of one rhamnose, one glucose, one glucuronic acid, one mannose and three galactose residues. This polymer is the most common exopolysaccharide produced by strains of the Burkholderia cepacia (Bcc) complex. One clinical strain produced also another polysaccharide constituted of three galactose units and one 3-deoxy-D-manno-2-octulosonic acid residues, a polymer that was previously isolated from two strains of B. cepacia genomovar I and B. cenocepacia IIIA.

Exopolysaccharides produced by a clinical strain of Burkholderia cepacia isolated from a cystic fibrosis patient

Burkholderia cepacia is an opportunistic pathogen involved in pulmonary infections related to cystic fibrosis. A clinical strain, BTS13, was isolated and the production of exopolysaccharides was tested growing the bacteria on two different media, one of which was rich in mannitol as carbon source. The primary structure of the polysaccharides was determined using mostly mass spectrometry and NMR spectroscopy. On both media an exopolysaccharide having the following repeating unit was produced: -->5)-beta-Kdop-(2-->3)-beta-D-Galp2Ac-(1-->4)-alpha-D-Galp-(1-->3)-beta-D-Galp-(1--> This polysaccharide has already been described as the biosynthetic product of another Burkholderia species, B. pseudomallei, the microbial agent causing melioidosis. In addition to this, when grown on the mannitol-rich medium, B. cepacia strain BTS13 produced another polysaccharide that was established to be levan: -->6)-beta-D-Fruf-(2-->. The content of levan was about 20% (w/w) of the total amount of polymers. The ability of B. cepacia to produce these two exopolysaccharides opens new perspectives in the investigation of the role of polysaccharides in lung infections.

Separation of 6-deoxy-heptan [correction of 6-deoxy-heptane] from a smooth-type lipopolysaccharide preparation of Burkholderia pseudomallei

Smooth-type lipopolysaccharide (LPS) of Burkholderia pseudomallei has been reported to contain two kinds of O-antigenic polysaccharides, a 1,3-linked homopolymer of 6-deoxy-heptose and a polymer with a repeating unit of -->3)-glucose-(1-->3)-6-deoxy-talose-(1--> with O-acetyl or O-methyl modifications. A LPS preparation containing these two polysaccharides was separated by gel-permeation chromatography in this study. Chemical analysis of the separated fractions revealed the 6-deoxy-heptan [corrected] to be a polysaccharide without a lipid portion and the polymer of glucose and 6-deoxy-talose to be an O-antigenic polysaccharide of the LPS. This result was further supported by the assay of these polysaccharide molecules for macrophage activation activity. The 6-deoxy-heptan [corrected] showed no macrophage activation, indicating that this polysaccharide was not the LPS, but one of the capsular polysaccharides of B. pseudomallei.

Detection of bacterial virulence genes by subtractive hybridization: identification of capsular polysaccharide of Burkholderia pseudomallei as a major virulence determinant

Burkholderia pseudomallei, the etiologic agent of melioidosis, is responsible for a broad spectrum of illnesses in humans and animals particularly in Southeast Asia and northern Australia, where it is endemic. Burkholderia thailandensis is a nonpathogenic environmental organism closely related to B. pseudomallei. Subtractive hybridization was carried out between these two species to identify genes encoding virulence determinants in B. pseudomallei. Screening of the subtraction library revealed A-T-rich DNA sequences unique to B. pseudomallei, suggesting they may have been acquired by horizontal transfer. One of the subtraction clones, pDD1015, encoded a protein with homology to a glycosyltransferase from Pseudomonas aeruginosa. This gene was insertionally inactivated in wild-type B. pseudomallei to create SR1015. It was determined by enzyme-linked immunosorbent assay and immunoelectron microscopy that the inactivated gene was involved in the production of a major surface polysaccharide. The 50% lethal dose (LD(50)) for wild-type B. pseudomallei is <10 CFU; the LD(50) for SR1015 was determined to be 3.5 x 10(5) CFU, similar to that of B. thailandensis (6.8 x 10(5) CFU). DNA sequencing of the region flanking the glycosyltransferase gene revealed open reading frames similar to capsular polysaccharide genes in Haemophilus influenzae, Escherichia coli, and Neisseria meningitidis. In addition, DNA from Burkholderia mallei and Burkholderia stabilis hybridized to a glycosyltransferase fragment probe, and a capsular structure was identified on the surface of B. stabilis via immunoelectron microscopy. Thus, the combination of PCR-based subtractive hybridization, insertional inactivation, and animal virulence studies has facilitated the identification of an important virulence determinant in B. pseudomallei.

Recovery of Burkholderia pseudomallei and B. cepacia from drinking water

Samples of drinking water were examined in order to evaluate the occurrence of two gram-negative bacteria: Burkholderia pseudomallei and B. cepacia. A total of 85 samples were collected from public and private buildings in the province of Bologna (Italy). Other bacteriological indicators (heterotrophic plate count at 22 and 36 degrees C) were also examined, together with physical and chemical parameters (temperature, pH, residual chlorine, total hardness and chemical oxygen demand (COD)). High levels of B. pseudomallei were recovered (mean value = 578 cfu/100 ml) in about 7% of samples, while B. cepacia was recovered in 3.5% (mean value = < 1) of the samples. The two microorganisms were found to correlate positively with heterotrophic plate counts at 22 and 36 degrees C, but not with the physical and chemical parameters taken into consideration.

Pathogenesis of and immunity to melioidosis

While Burkholderia pseudomallei, the causative agent of melioidosis, is becoming increasingly recognized as a significant cause of morbidity and mortality in regions to which it is endemic, no licensed vaccine preparation currently exists for immunization against the disease. Therefore, one of the primary goals of our research has been to identify and characterize antigens expressed by B. pseudomallei isolates for the intended purpose of developing a vaccine construct that can be used to actively immunize specific high risk populations against the disease. By utilizing a combination of biochemical, immunological and molecular approaches, our studies now indicate that some of the most promising candidates for this task include flagellin proteins and the endotoxin derived O-polysaccharide (PS) antigens expressed by the organism. In this review, we have attempted to summarize the current status of B. pseudomallei research while endeavoring to provide a rationale for our approach towards the development of a melioidosis vaccine.

Shedding of lipopolysaccharide and 200-kDa surface antigen during the in vitro growth of virulent Ara- and avirulent Ara+ Burkholderia pseudomallei

Non-virulent Ara+ B. pseudomallei environmental isolates differ from virulent Ara- clinical isolates by their ability to assimilate L-arabinose and the absence of a 200 kDa antigen on their surface. The latter, present only on the Ara- isolates from either clinical or environmental origin, was recently demonstrated by its immunoreactivity with monoclonal antibody (MAb) 5F8. We recently demonstrated that lipopolysaccharide (LPS) from both biotypes were indistinguishable from one another with regard to SDS-PAGE profiles and immunoreactivities with immune sera. In this study, the shedding of LPS and 200-kDa antigen into the culture medium during the in vitro growth of Ara- was compared with that of its Ara+ counterpart, using MAb-based sandwich ELISAs. The results showed that the LPS shedding profiles from the two biotypes were similar to one another. This was in contrast to the situation with the 5F8-reactive antigen. The culture fluid of all Ara- isolates and none of the Ara+ isolates were found to react strongly with the MAb 5F8 during the early log phase of growth. However, during the late stationary phase, a trace amount of the 5F8-reactive material could also be detected in the culture fluid of the Ara+ isolates.

Convenient and versatile DNA extraction using agarose plugs for ribotyping of problematic bacterial species

We describe a convenient, versatile and safe method for preparing bacterial DNA for ribotyping analysis. In this method, extraction of bacterial DNA from Salmnonella typhi and Burkholderia pseudomallei. and subsequent restriction endonuclease digestion, was performed in agarose blocks/plugs thus minimizing shearing and loss of DNA, problems commonly associated with liquid phase phenol extraction. Digested DNA in the plugs was then electrophoresed directly, transferred to nylon membranes and hybridized with labeled rDNA probes in the usual manner to provide reproducible restriction patterns. This method is particularly useful for bacterial species where standard DNA extraction in the liquid phase using phenol has been problematic (e.g. B. pseudomallei) but can be used for any bacterial species. The DNA extracted within the agarose plugs can be stored for long periods and can be used in other, widely-used typing methods such as pulsed-field gel electrophoresis (PFGE) and PCR-based techniques. Embedding live cells directly in agarose plugs also minimizes the risk of exposure to these virulent human pathogens among laboratory workers.

Antigenic differences between clinical and environmental isolates of Burkholderia pseudomallei

Burkholderia pseudomallei is a free-living organism that causes the potentially lethal tropical infection melioidosis. The disease is endemic in many parts of eastern Asia and northern Australia. The presence of two distinct biotypes in soil can be reliably distinguished by their ability to assimilate L-arabinose. Whereas some soil isolates could utilize this substrate (Ara+), the remaining soil isolates and all clinical isolates tested so far could not (Ara-). Only the Ara- isolates were virulent in animal models. We have raised a murine monoclonal antibody (MAb) that can readily distinguish Ara- from Ara+ biotypes. The MAb reacted with a high molecular weight component present only on the Ara- biotype. With this MAb, clinical and soil Ara- isolates gave identical positive reactions in agglutination, immunofluorescence, ELISA and immunoblot assays. Using these same assay systems, the soil Ara+ biotype did not react with the MAb. Similar but distinct immunoblot patterns were also noted when these two Ara biotypes were probed with sera from patients with melioidosis or with polyclonal immune rabbit sera. These data showed that the Ara- biotype from both clinical and environmental isolates is antigenically different from its Ara+ environmental counterpart. The SDS-PAGE protein and lectin-binding profiles of both groups of Ara- isolates were also found to be different from those of the Ara+ biotype.

Characterization of three capsular polysacharides produced by Burkholderia pseudomallei

Three kinds of capsular polysaccharide (CP) were found to be produced by Burkholderia pseudomallei. When the bacterium was grown with the medium without glycerol, CP-1a and CP-1b were produced. CP-1a was mainly 1.4-linked glucan and CP-1b was identified as a polymer composed of galactose and 3-deoxy-D-manno-octulosonic acid, whose chemical structure was recently reported by other laboratories. When the bacterium was grown with the medium containing 5" glycerol. CP-2 was synthesized. CP-2 contained galactose, rhamnose, mannose, glucose and a uronic acid in a ratio of approximately 3:1:0.3:1:1. Methylation analysis of the purified polysaccharides demonstrated that the two acidic polysaccharides. CP-1b and CP-2 shared no common structure, indicating that CP-2 was an acidic capsular polysaccharide whose chemical characters were not reported previously.

The type II O-antigenic polysaccharide moiety of Burkholderia pseudomallei lipopolysaccharide is required for serum resistance and virulence

Melioidosis, an infection caused by the gram-negative bacterial pathogen Burkholderia pseudomallei, is endemic in south-east Asia and northern Australia. Acute septicaemic melioidosis is a major cause of morbidity and mortality, especially in north-east Thailand. B. pseudomallei is highly resistant to the bactericidal activity of normal human serum (NHS), and we have found that B. pseudomallei 1026b multiplies in 10-30% NHS. We developed a simple screen for the identification of serum-sensitive mutants based on this novel phenotype. Approximately 1200 Tn5-OT182 mutants were screened, and three serum-sensitive mutants were identified. The type II O-antigenic polysaccharide (O-PS) moiety of lipopolysaccharide was not present in the serum-sensitive mutants. A representative serum-sensitive mutant, SRM117, was killed by the alternative pathway of complement and was less virulent than 1026b in three animal models of melioidosis. The Tn5-OT182 integrations in the serum-sensitive mutants were physically linked on the B. pseudomallei chromosome, and further genetic analysis of this locus revealed a cluster of 15 genes required for type II O-PS production. The proteins encoded by these genes were similar to proteins involved in bacterial polysaccharide biosynthesis. The results presented here demonstrate that type II O-PS is essential for B. pseudomallei serum resistance and virulence.