Layering vaccination with antibiotic therapy results in protection and clearance of Burkholderia pseudomallei in Balb/c mice

Melioidosis is a disease that is difficult to treat due to the causative organism, Burkholderia pseudomallei being inherently antibiotic resistant and it having the ability to invade, survive, and replicate in an intracellular environment. Combination therapy approaches are routinely being evaluated in animal models with the aim of improving the level of protection and clearance of colonizing bacteria detected. In this study, a subunit vaccine layered with the antibiotic finafloxacin was evaluated in vivo against an inhalational infection with B. pseudomallei in Balb/c mice. Groups of mice vaccinated, infected, and euthanized at antibiotic initiation had a reduced bacterial load compared to those that had not been immunized. In addition, the subunit vaccine provided a synergistic effect when it was delivered with a CpG ODN and finafloxacin was initiated at 48 h post-challenge. Vaccination was also shown to improve the outcome, in a composite measure of survival and clearance. In summary, layering a subunit vaccine with the antibiotic finafloxacin is a promising therapeutic alternative for use in the treatment of B. pseudomallei infections.

Differences in the gut microbiota between Gurkhas and soldiers of British origin

Previous work indicated that the incidence of travellers' diarrhoea (TD) is higher in soldiers of British origin, when compared to soldiers of Nepalese descent (Gurkhas). We hypothesise that the composition of the gut microbiota may be a contributing factor in the risk of developing TD in soldiers of British origin. This study aimed to characterise the gut microbial composition of Gurkha and non-Gurkha soldiers of the British Army. Recruitment of 38 soldiers (n = 22 Gurkhas, n = 16 non-Gurkhas) and subsequent stool collection, enabled shotgun metagenomic sequencing-based analysis of the gut microbiota. The microbiota of Gurkhas had significantly (P < 0.05) lower diversity, for both Shannon and Simpson diversity indices, using species level markers than the gut microbiota of non-Gurkha soldiers. Non-metric Multidimensional Scaling (NMDS) of the Bray-Curtis distance matrix revealed a significant difference in the composition of the gut microbiota between Gurkhas and non-Gurkha soldiers, at both the species level (P = 0.0178) and the genus level (P = 0.0483). We found three genera and eight species that were significantly enriched in the non-Gurkha group and one genus (Haemophilus) and one species (Haemophilus parainfluenzae) which were enriched in the Gurkha group. The difference in the microbiota composition between Gurkha soldiers and soldiers of British origin may contribute to higher colonization resistance against diarrhoeal pathogens in the former group. Our findings may enable further studies into interventions that modulate the gut microbiota of soldiers to prevent TD during deployment.

Slow growing bacteria survive bacteriophage in isolation

The interactions between bacteria and bacteriophage have important roles in the global ecosystem; in turn changes in environmental parameters affect the interactions between bacteria and phage. However, there is a lack of knowledge on whether clonal bacterial populations harbour different phenotypes that respond to phage in distinct ways and whether the abundance of such phenotypes within bacterial populations is affected by variations in environmental parameters. Here we study the impact of variations in nutrient availability, bacterial growth rate and phage abundance on the interactions between the phage T4 and individual Escherichia coli cells confined in spatial refuges. Surprisingly, we found that fast growing bacteria survive together with all of their clonal kin cells, whereas slow growing bacteria survive in isolation. We also discovered that the number of bacteria that survive in isolation decreases at increasing phage doses possibly due to lysis inhibition in the presence of secondary adsorptions. We further show that these changes in the phenotypic composition of the E. coli population have important consequences on the bacterial and phage population dynamics and should therefore be considered when investigating bacteria-phage interactions in ecological, health or food production settings in structured environments.

In Vitro Activity of Finafloxacin against Panels of Respiratory Pathogens

This study determined the in vitro activity of finafloxacin against panels of bacterial strains, representative of those associated with infection in cystic fibrosis patients and predominately isolated from clinical cases of respiratory disease. Many of these isolates were resistant to various antimicrobials evaluated including the aminoglycosides, cephalosporins, carbapenems and fluoroquinolones. Broth microdilution assays were performed at neutral and acidic pH, to determine antimicrobial activity. Finafloxacin demonstrated superior activity at reduced pH for all of the bacterial species investigated, highlighting the requirement to determine the activity of antimicrobials in host-relevant conditions.

In Vitro Activity of Novel Topoisomerase Inhibitors against Francisella tularensis and Burkholderia pseudomallei

Antimicrobial resistance is a global issue, and the investigation of alternative therapies that are not traditional antibiotics are warranted. Novel bacterial type II topoisomerase inhibitors (NBTIs) have recently emerged as a novel class of antibiotics with reduced potential for cross-resistance to fluoroquinolones due to their novel mechanism of action. This study investigated the in vitro activity of a series of cyclohexyl-oxazolidinone bacterial topoisomerase inhibitors against type strains of Francisella tularensis and Burkholderia pseudomallei. Broth microdilution, time-kill, and cell infection assays were performed to determine activity against these biothreat pathogens. Two candidates were identified that demonstrated in vitro activity in multiple assays that in some instances was equivalent to ciprofloxacin and doxycycline. These data warrant the further evaluation of these novel NBTIs and future iterations in vitro and in vivo.

Using a multi-omic approach to investigate the mechanism of 12-bis-THA activity against Burkholderia thailandensis

Burkholderia pseudomallei is the causative agent of the tropical disease, melioidosis. It is intrinsically resistant to many antimicrobials and treatment requires an onerous regimen of intravenous and orally administered drugs. Relapse of disease and high rates of mortality following treatment are common, demonstrating the need for new anti-Burkholderia agents. The cationic bola-amphiphile, 12,12'-(dodecane-1,12-diyl) bis (9-amino-1,2,3,4-tetrahydroacridinium), referred to as 12-bis-THA, is a molecule with the potential to treat Burkholderia infections. 12-bis-THA spontaneously forms cationic nanoparticles that bind anionic phospholipids in the prokaryotic membrane and are readily internalized. In this study, we examine the antimicrobial activity of 12-bis-THA against strains of Burkholderia thailandensis. As B. pseudomallei produces a polysaccharide capsule we first examined if this extra barrier influenced the activity of 12-bis-THA which is known to act on the bacterial envelope. Therefore two strains of B. thailandensis were selected for further testing, strain E264 which does not produce a capsule and strain E555 which does produce a capsule that is chemically similar to that found in B. pseudomallei. In this study no difference in the minimum inhibitory concentration (MIC) was observed when capsulated (E555) and unencapsulated (E264) strains of B. thailandensis were compared, however time-kill analysis showed that the unencapsulated strain was more susceptible to 12-bis-THA. The presence of the capsule did not affect the membrane permeation of 12-bis-THA at MIC concentrations. Proteomic and metabolomic analyses showed that 12-bis-THA causes a shift in central metabolism away from glycolysis and glyoxylate cycle, and suppressed the production of the F₁ domain of ATP synthase. In summary, we provide insight into the molecular mechanisms underpinning the activity of 12-bis-THA against B. thailandensis and discuss its potential for further development.

The BALB/c Mouse Model for the Evaluation of Therapies to Treat Infections with Aerosolized Burkholderia pseudomallei

Burkholderia pseudomallei, the causative agent of the disease melioidosis, has been isolated from the environment in 45 countries. The treatment of melioidosis is complex, requiring lengthy antibiotic regimens, which can result in the relapse of the disease following treatment cessation. It is important that novel therapies to treat infections with B. pseudomallei be assessed in appropriate animal models, and discussions regarding the different protocols used between laboratories are critical. A ‘deep dive’ was held in October 2020 focusing on the use of the BALB/c mouse model and the inhalational route of infection to evaluate new antibiotic therapies.

Efficacy of finafloxacin in a murine model of inhalational glanders

Burkholderia mallei, the causative agent of glanders, is principally a disease of equines, although it can also infect humans and is categorized by the U.S. Centers for Disease Control and Prevention as a category B biological agent. Human cases of glanders are rare and thus there is limited information on treatment. It is therefore recommended that cases are treated with the same therapies as used for melioidosis, which for prophylaxis, is co-trimoxazole (trimethoprim/sulfamethoxazole) or co-amoxiclav (amoxicillin/clavulanic acid). In this study, the fluoroquinolone finafloxacin was compared to co-trimoxazole as a post-exposure prophylactic in a murine model of inhalational glanders. BALB/c mice were exposed to an aerosol of B. mallei followed by treatment with co-trimoxazole or finafloxacin initiated at 24 h post-challenge and continued for 14 days. Survival at the end of the study was 55% or 70% for mice treated with finafloxacin or co-trimoxazole, respectively, however, this difference was not significant. However, finafloxacin was more effective than co-trimoxazole in controlling bacterial load within tissues and demonstrating clearance in the liver, lung and spleen following 14 days of therapy. In summary, finafloxacin should be considered as a promising alternative treatment following exposure to B. mallei.

Investigation of a combination therapy approach for the treatment of melioidosis

The efficacy of finafloxacin as a component of a layered defense treatment regimen was determined in vitro and in vivo against an infection with Burkholderia pseudomallei. Doxycycline was down-selected from a panel of antibiotics evaluated in vitro and used in combination with finafloxacin in a Balb/c mouse model of inhalational melioidosis. When treatment was initiated at 24 h post-infection with B. pseudomallei, there were no differences in the level of protection offered by finafloxacin or doxycycline (as monotherapies) when compared to the combination therapy. There was evidence for improved bacterial control in the groups treated with finafloxacin (as monotherapies or in combination with doxycycline) when compared to mice treated with doxycycline. Survival comparisons of finafloxacin and doxycycline (as monotherapies) or in combination initiated at 36 h post-infection indicated that finafloxacin was superior to doxycycline. Doxycycline was also unable to control the levels of bacteria within tissues to the extent that doxycycline and finafloxacin used in combination or finafloxacin (as a sole therapy) could. In summary, finafloxacin is a promising therapy for use in the event of exposure to B. pseudomallei.

Generation of Distinct Differentially Culturable Forms of Burkholderia following Starvation at Low Temperature

Bacteria have developed unique mechanisms to adapt to environmental stresses and challenges of the immune system. Here, we report that Burkholderia pseudomallei, the causative agent of melioidosis, and its laboratory surrogate, Burkholderia thailandensis, utilize distinct mechanisms for surviving starvation at different incubation temperatures. At 21°C, Burkholderia are present as short rods which can rapidly reactivate and form colonies on solid media. At 4°C, Burkholderia convert into coccoid forms that cannot be cultured on solid agar but can be resuscitated in liquid media supplemented with supernatant obtained from logarithmic phase cultures of B. thailandensis, or catalase and Tween 80, thus displaying characteristics of differentially culturable bacteria (DCB). These DCB have low intensity fluorescence when stained with SYTO 9, have an intact cell membrane (propidium iodide negative), and contain 16S rRNA at levels comparable with growing cells. We also present evidence that lytic transglycosylases, a family of peptidoglycan-remodeling enzymes, are involved in the generation of coccoid forms and their resuscitation to actively growing cells. A B. pseudomallei ΔltgGCFD mutant with four ltg genes deleted did not produce coccoid forms at 4°C and could not be resuscitated in the liquid media evaluated. Our findings provide insights into the adaptation of Burkholderia to nutrient limitation and the generation of differentially culturable bacteria. IMPORTANCE Bacterial pathogens exhibit physiologically distinct forms that enable their survival in an infected host, the environment and following exposure to antimicrobial agents. B. pseudomallei causes the disease melioidosis, which has a high mortality rate and is difficult to treat with antibiotics. The bacterium is endemic to several countries and detected in high abundance in the environment. Here, we report that during starvation at low temperature, B. pseudomallei produces coccoid forms that cannot grow in standard media and which, therefore, can be challenging to detect using common tools. We provide evidence that the formation of these cocci is mediated by cell wall-specialized enzymes and lytic transglycosylases, and that resuscitation of these forms occurs following the addition of catalase and Tween 80. Our findings have important implications for the disease control and detection of B. pseudomallei, an agent of both public health and defense interest.

Finafloxacin, a Novel Fluoroquinolone, Reduces the Clinical Signs of Infection and Pathology in a Mouse Model of Q Fever

Finafloxacin is a novel fluoroquinolone with optimal antibacterial activity in low pH environments, therefore offering a therapeutic advantage over some traditional antibiotics, in treating bacterial infections associated with acidic foci. Coxiella burnetii, the causative agent of Q fever, is a bacterium which resides and replicates in acidic intracellular parasitic vacuoles. The efficacy of finafloxacin was evaluated in vivo using the A/J mouse model of inhalational Q fever and was compared to doxycycline, the standard treatment for this infection and ciprofloxacin, a comparator fluoroquinolone. Finafloxacin reduced the severity of the clinical signs of infection and weight loss associated with Q fever, but did not reduce the level of bacterial colonization in tissues compared to doxycycline or ciprofloxacin. However, histopathological analysis suggested that treatment with finafloxacin reduced tissue damage associated with C. burnetii infection. In addition, we report for the first time, the use of viable counts on axenic media to evaluate antibiotic efficacy in vivo.

Individual bacteria in structured environments rely on phenotypic resistance to phage

Bacteriophages represent an avenue to overcome the current antibiotic resistance crisis, but evolution of genetic resistance to phages remains a concern. In vitro, bacteria evolve genetic resistance, preventing phage adsorption or degrading phage DNA. In natural environments, evolved resistance is lower possibly because the spatial heterogeneity within biofilms, microcolonies, or wall populations favours phenotypic survival to lytic phages. However, it is also possible that the persistence of genetically sensitive bacteria is due to less efficient phage amplification in natural environments, the existence of refuges where bacteria can hide, and a reduced spread of resistant genotypes. Here, we monitor the interactions between individual planktonic bacteria in isolation in ephemeral refuges and bacteriophage by tracking the survival of individual cells. We find that in these transient spatial refuges, phenotypic resistance due to reduced expression of the phage receptor is a key determinant of bacterial survival. This survival strategy is in contrast with the emergence of genetic resistance in the absence of ephemeral refuges in well-mixed environments. Predictions generated via a mathematical modelling framework to track bacterial response to phages reveal that the presence of spatial refuges leads to fundamentally different population dynamics that should be considered in order to predict and manipulate the evolutionary and ecological dynamics of bacteria–phage interactions in naturally structured environments.

Bacteriophages represent a promising avenue to overcome the current antibiotic resistance crisis, but evolution of phage resistance remains a concern. This study shows that in the presence of spatial refuges, genetic resistance to phage is less of a problem than commonly assumed, but the persistence of genetically susceptible bacteria suggests that eradicating bacterial pathogens from structured environments may require combined phage-antibiotic therapies.

A systematic review of the effect of dietary pulses on microbial populations inhabiting the human gut

Pulses are dry leguminous crops consisting of beans, lentils, chickpeas, and peas. They are a broad category of food that are often aggregated when their contribution to healthy dietary patterns are disseminated. However, the different genera and varieties of pulses vary in composition and are consumed in different amounts, largely dictated by geographic region and ethnicity. Given the number of pulse-derived components, including fibre, that have the capacity to alter the composition of the gut microbiome, the objective of this study was to systematically review dietary pulses and pulse-derived ingredients as a broader food group, to determine their effect on gut microbiota in humans. Major scientific databases were used to conduct the search, which spanned from 1990 until February 2019. The search strategy identified 2,444 articles and five studies were included in this analysis. Two studies used whole pulses (chickpeas and pinto beans), one study used cooked navy bean powder, and the two remaining studies used pulse-derived fibre (lupin or yellow pea hulls). Although inconsistent, some studies demonstrated that whole pulses (pinto beans and chickpeas), cooked navy bean powder, and pulse-derived fibre (lupin kernel fibre), did impose changes to the microbiota that inhabit the human large intestine. However, there was considerable variability concerning the methodologies and endpoints used to decipher the observed effects on the abundance, diversity, and/or richness of specific microbiota or the microbiome. More extensive human studies that directly link the effects of specific types of pulses on the gastrointestinal microbial environment to health outcomes in the host are required.

The lytic transglycosylase, LtgG, controls cell morphology and virulence in Burkholderia pseudomallei

Burkholderia pseudomallei is the causative agent of the tropical disease melioidosis. Its genome encodes an arsenal of virulence factors that allow it, when required, to switch from a soil dwelling bacterium to a deadly intracellular pathogen. With a high intrinsic resistance to antibiotics and the ability to overcome challenges from the host immune system, there is an increasing requirement for new antibiotics and a greater understanding into the molecular mechanisms of B. pseudomallei virulence and dormancy. The peptidoglycan remodeling enzymes, lytic transglycosylases (Ltgs) are potential targets for such new antibiotics. Ltgs cleave the glycosidic bonds within bacterial peptidoglycan allowing for the insertion of peptidoglycan precursors during cell growth and division, and cell membrane spanning structures such as flagella and secretion systems. Using bioinformatic analysis we have identified 8 putative Ltgs in B. pseudomallei K96243. We aimed to investigate one of these Ltgs, LtgG (BPSL3046) through the generation of deletion mutants and biochemical analysis. We have shown that LtgG is a key contributor to cellular morphology, division, motility and virulence in BALB/c mice. We have determined the crystal structure of LtgG and have identified various amino acids likely to be important in peptidoglycan binding and catalytic activity. Recombinant protein assays and complementation studies using LtgG containing a site directed mutation in aspartate 343, confirmed the essentiality of this amino acid in the function of LtgG.

The Fluoroquinolone Finafloxacin Protects BALB/c Mice Against an Intranasal Infection With Francisella tularensis Strain SchuS4

The efficacy of the novel fluoroquinolone finafloxacin was evaluated as a potential therapeutic in vitro and in vivo, following an intranasal infection of Francisella tularensis strain SchuS4 in BALB/c mice. We demonstrated that short treatment courses of finafloxacin provide high levels of protection, with a single dose resulting in a significant increase in time to death when compared to ciprofloxacin. In addition, following investigation into the window of opportunity for treatment, we have shown that finafloxacin can provided protection when administered up to 96 h post-challenge. This is particularly encouraging since mice displayed severe signs of disease at this time point. In summary, finafloxacin may be a promising therapy for use in the event of exposure to F. tularensis, perhaps enabling the treatment regimen to be shortened or if therapy is delayed. The efficacy of finafloxacin against other biological threat agents also warrants investigation.

Inhaled Liposomal Ciprofloxacin Protects against a Lethal Infection in a Murine Model of Pneumonic Plague

Inhalation of Yersinia pestis can lead to pneumonic plague, which without treatment is inevitably fatal. Two novel formulations of liposome-encapsulated ciprofloxacin, ‘ciprofloxacin for inhalation’ (CFI, Lipoquin^®) and ‘dual release ciprofloxacin for inhalation’ (DRCFI, Pulmaquin^®) containing CFI and ciprofloxacin solution, are in development. These were evaluated as potential therapies for infection with Y. pestis. In a murine model of pneumonic plague, human-like doses of aerosolized CFI, aerosolized DRCFI or intraperitoneal (i.p.) ciprofloxacin were administered at 24 h (representing prophylaxis) or 42 h (representing treatment) post-challenge. All three therapies provided a high level of protection when administered 24 h post-challenge. A single dose of CFI, but not DRCFI, significantly improved survival compared to a single dose of ciprofloxacin. Furthermore, single doses of CFI and DRCFI reduced bacterial burden in lungs and spleens to below the detectable limit at 60 h post-challenge. When therapy was delayed until 42 h post-challenge, a single dose of CFI or DRCFI offered minimal protection. However, single doses of CFI or DRCFI were able to significantly reduce the bacterial burden in the spleen compared to empty liposomes. A three-day treatment regimen of ciprofloxacin, CFI, or DRCFI resulted in high levels of protection (90–100% survival). This study suggests that CFI and DRCFI may be useful therapies for Y. pestis infection, both as prophylaxis and for the treatment of plague.

The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis

BACKGROUND/OBJECTIVES

It is unknown whether short sleep duration causatively contributes to weight gain. Studies investigating effects of partial sleep deprivation (PSD) on energy balance components report conflicting findings. Our objective was to conduct a systematic review and meta-analysis of human intervention studies assessing the effects of PSD on energy intake (EI) and energy expenditure (EE).

SUBJECTS/METHODS

EMBASE, Medline, Cochrane CENTRAL, Web of Science and Scopus were searched. Differences in EI and total EE following PSD compared with a control condition were generated using the inverse variance method with random-effects models. Secondary outcomes included macronutrient distribution and resting metabolic rate. Heterogeneity was quantified with the I²-statistic.

RESULTS

Seventeen studies (n=496) were eligible for inclusion in the systematic review, and 11 studies (n=172) provided sufficient data to be included in meta-analyses. EI was significantly increased by 385 kcal (95% confidence interval: 252, 517; P<0.00001) following PSD compared with the control condition. We found no significant change in total EE or resting metabolic rate as a result of PSD. The observed increase in EI was accompanied by significantly higher fat and lower protein intakes, but no effect on carbohydrate intake.

CONCLUSIONS

The pooled effects of the studies with extractable data indicated that PSD resulted in increased EI with no effect on EE, leading to a net positive energy balance, which in the long term may contribute to weight gain.

Health claims using the term 'sustained energy' are trending but glycaemic response data are being used to support: is this misleading without context?

One of the most recent food trends is the quest for products that provide 'sustained energy'; a term that is garnering considerable attention within the marketplace. Often, 'sustained energy' health claims are based on a food's post-prandial glycaemic response. However, are generalised health claims regarding 'sustained energy' valid when only supported by glycaemic response data? Without context, the short answer is: probably not. Health claims that link sustained energy to a glycaemic response, or any other attribute of a food or diet, require context to ensure that the public correctly interprets and experiences the claimed effect and is not misled in their quest for healthy foods that impose the desired physiological benefit.

The anticancer gene ORCTL3 targets stearoyl-CoA desaturase-1 for tumour-specific apoptosis

ORCTL3 is a member of a group of genes, the so-called anticancer genes, that cause tumour-specific cell death. We show that this activity is triggered in isogenic renal cells upon their transformation independently of the cells' proliferation status. For its cell death effect ORCTL3 targets the enzyme stearoyl-CoA desaturase-1 (SCD1) in fatty acid metabolism. This is caused by transmembrane domains 3 and 4, which are more efficacious in vitro than a low molecular weight drug against SCD1, and critically depend on their expression level. SCD1 is found upregulated upon renal cell transformation indicating that its activity, while not impacting proliferation, represents a critical bottleneck for tumourigenesis. An adenovirus expressing ORCTL3 leads to growth inhibition of renal tumours in vivo and to substantial destruction of patients' kidney tumour cells ex vivo. Our results indicate fatty acid metabolism as a target for tumour-specific apoptosis in renal tumours and suggest ORCTL3 as a means to accomplish this.

Assessment of antimicrobial peptide LL-37 as a post-exposure therapy to protect against respiratory tularemia in mice

Early activation of the innate immune response is important for protection against infection with Francisella tularensis live vaccine strain (LVS) in mice. The human cathelicidin antimicrobial peptide LL-37 is known to have immunomodulatory properties, and therefore exogenously administered LL-37 may be suitable as an early post-exposure therapy to protect against LVS infection. LL-37 has been evaluated for immunostimulatory activity in uninfected mice and for activity against LVS in macrophage assays and protective efficacy when administered post-challenge in a mouse model of respiratory tularemia. Increased levels of pro-inflammatory cytokine IL-6, chemokines monocyte chemoattractant protein 1 (MCP-1) and CXCL1 with increased neutrophil influx into the lungs were observed in uninfected mice after intranasal administration of LL-37. Following LVS challenge, LL-37 administration resulted in increased IL-6, IL-12 p70, IFNγ and MCP-1 production, a slowing of LVS growth in the lung, and a significant extension of mean time to death compared to control mice. However, protection was transient, with the LL-37 treated mice eventually succumbing to infection. As this short course of nasally delivered LL-37 was moderately effective at overcoming the immunosuppressive effects of LVS infection this suggests that a more sustained treatment regimen may be an effective therapy against this pathogen.

A Burkholderia pseudomallei toxin inhibits helicase activity of translation factor eIF4A

The structure of BPSL1549, a protein of unknown function from Burkholderia pseudomallei, reveals a similarity to Escherichia coli cytotoxic necrotizing factor 1. We found that BPSL1549 acted as a potent cytotoxin against eukaryotic cells and was lethal when administered to mice. Expression levels of bpsl1549 correlate with conditions expected to promote or suppress pathogenicity. BPSL1549 promotes deamidation of glutamine-339 of the translation initiation factor eIF4A, abolishing its helicase activity and inhibiting translation. We propose to name BPSL1549 Burkholderia lethal factor 1.

The cluster 1 type VI secretion system is a major virulence determinant in Burkholderia pseudomallei

The Burkholderia pseudomallei K96243 genome encodes six type VI secretion systems (T6SSs), but little is known about the role of these systems in the biology of B. pseudomallei. In this study, we purified recombinant Hcp proteins from each T6SS and tested them as vaccine candidates in the BALB/c mouse model of melioidosis. Recombinant Hcp2 protected 80% of mice against a lethal challenge with K96243, while recombinant Hcp1, Hcp3, and Hcp6 protected 50% of mice against challenge. Hcp6 was the only Hcp constitutively produced by B. pseudomallei in vitro; however, it was not exported to the extracellular milieu. Hcp1, on the other hand, was produced and exported in vitro when the VirAG two-component regulatory system was overexpressed in trans. We also constructed six hcp deletion mutants (Δhcp1 through Δhcp6) and tested them for virulence in the Syrian hamster model of infection. The 50% lethal doses (LD(50)s) for the Δhcp2 through Δhcp6 mutants were indistinguishable from K96243 (<10 bacteria), but the LD(50) for the Δhcp1 mutant was >10(3) bacteria. The hcp1 deletion mutant also exhibited a growth defect in RAW 264.7 macrophages and was unable to form multinucleated giant cells in this cell line. Unlike K96243, the Δhcp1 mutant was only weakly cytotoxic to RAW 264.7 macrophages 18 h after infection. The results suggest that the cluster 1 T6SS is essential for virulence and plays an important role in the intracellular lifestyle of B. pseudomallei.

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.

CD4+ T-cell immunity to the Burkholderia pseudomallei ABC transporter LolC in melioidosis

Burkholderia pseudomallei causes melioidosis, a disease with a wide range of possible outcomes, from seroconversion and dormancy to sepsis and death. This spectrum of host-pathogen interactions poses challenging questions about the heterogeneity in immunity to B. pseudomallei. Models show protection to be dependent on CD4(+) cells and IFN-γ, but little is known about specific target antigens. Having previously implicated the ABC transporter, LolC, in protective immunity, we here use epitope prediction, HLA-binding studies, HLA-transgenic models and studies of T cells from seropositive individuals to characterize HLA-restricted LolC responses. Immunized mice showed long-lasting memory to the protein, whereas predictive algorithms identified epitopes within LolC that subsequently demonstrated strong HLA class II binding. Immunization of HLA-DR transgenics with LolC stimulated T-cell responses to four of these epitopes. Furthermore, the responsiveness of HLA transgenics to LolC revealed a hierarchy supportive of HLA polymorphism-determined differential susceptibility. Seropositive human donors of diverse HLA class II types showed T-cell responses to LolC epitopes, which are conserved among Burkholderia species including Burkholderia cenocepacia, associated with life-threatening cepacia complex in cystic fibrosis patients and Burkholderia mallei, which causes glanders. These findings suggest a role for LolC epitopes in multiepitope vaccine design for melioidosis and related diseases.

Lipopolysaccharide from Burkholderia thailandensis E264 provides protection in a murine model of melioidosis

Burkholderia thailandensis is a less virulent close relative of Burkholderia pseudomallei, a CDC category B biothreat agent. We have previously shown that lipopolysaccharide (LPS) extracted from B. pseudomallei can provide protection against a lethal challenge of B. pseudomallei in a mouse model of melioidosis. Sugar analysis on LPS from B. thailandensis strain E264 confirmed that this polysaccharide has a similar structure to LPS from B. pseudomallei. Mice were immunised with LPS from B. thailandensis or B. pseudomallei and challenged with a lethal dose of B. pseudomallei strain K96243. Similar protection levels were observed when either LPS was used as the immunogen. This data suggests that B. thailandensis LPS has the potential to be used as part of a subunit based vaccine against pathogenic B. pseudomallei.

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.

The identification of surface proteins of Burkholderia pseudomallei

Burkholderia pseudomallei, the causative agent of the disease melioidosis is a human pathogen endemic in Northern Australia and South-East Asia. At present there is no available vaccine or effective treatment for this disease. Surface proteins play crucial roles in the host-pathogen interaction and have been exploited as vaccine candidates and diagnostic targets. Therefore, we wished to identify immunogenic surface proteins of B. pseudomallei. To this end we used two proteomic-based approaches in parallel: a biotinylation approach for the detection of surface located proteins identified 35 proteins, while screening with human sera identified 12 immunogenic proteins. Nine of these proteins were identified by both methods indicating that they may be both surface located and immunogenic: these proteins will be evaluated further as vaccine candidates and diagnostic targets.

Global map of growth-regulated gene expression in Burkholderia pseudomallei, the causative agent of melioidosis

Many microbial pathogens express specific virulence traits at distinct growth phases. To understand the molecular pathways linking bacterial growth to pathogenicity, we have characterized the growth transcriptome of Burkholderia pseudomallei, the causative agent of melioidosis. Using a fine-scale sampling approach, we found approximately 17% of all B. pseudomallei genes displaying regulated expression during growth in rich medium, occurring as broad waves of functionally coherent gene expression tightly associated with distinct growth phases and transition points. We observed regulation of virulence genes across all growth phases and identified serC as a potentially new virulence factor by virtue of its coexpression with other early-phase virulence genes. serC-disrupted B. pseudomallei strains were serine auxotrophs and in mouse infection assays exhibited a dramatic attenuation of virulence compared to wild-type B. pseudomallei. Immunization of mice with serC-disrupted B. pseudomallei also conferred protection against subsequent challenges with different wild-type B. pseudomallei strains. At a genomic level, early-phase genes were preferentially localized on chromosome 1, while stationary-phase genes were significantly biased towards chromosome 2. We detected a significant level of chromosomally clustered gene expression, allowing us to predict approximately 100 potential operons in the B. pseudomallei genome. We computationally and experimentally validated these operons by showing that genes in these regions are preferentially transcribed in the same 5'-->3' direction, possess significantly shorter intergenic lengths than the overall genome, and are expressed as a common mRNA transcript. The availability of this transcriptome map provides an important resource for understanding the transcriptional architecture of B. pseudomallei.

The nematodePanagrellus redivivusis susceptible to killing by human pathogens at 37 °C

Caenorhabditis elegans has been used as a host for the study of bacteria that cause disease in mammals. However, a significant limitation of the model is that C. elegans is not viable at 37 degrees C. We report that the gonochoristic nematode Panagrellus redivivus survives at 37 degrees C and maintains its life cycle at temperatures up to and including 31.5 degrees C. The C. elegans pathogens Pseudomonas aeruginosa, Salmonella enterica, Staphylococcus aureus, but not Yersinia pseudotuberculosis, reduced P. redivivus lifespan. Of four strains of Burkholderia multivorans tested, one reduced P. redivivus lifespan at both temperatures, one was avirulent at both temperatures and two strains reduced P. redivivus lifespan only at 37 degrees C. The mechanism by which one of these strains killed P. redivivus at 37 degrees C, but not at 25 degrees C, was investigated further. Killing required viable bacteria, did not involve bacterial invasion of tissues, is unlikely to be due to a diffusible, bacterial toxin and was not associated with increased numbers of live bacteria within the intestine of the worm. We believe B. multivorans may kill P. redivivus by a temperature-regulated mechanism similar to B. pseudomallei killing of C. elegans.

Age influences resistance of Caenorhabditis elegans to killing by pathogenic bacteria

Caenorhabditis elegans has previously been proposed as an alternative host for models of infectious disease caused by human pathogens. When exposed to some human pathogenic bacteria, the life span of nematodes is significantly reduced. We have shown that mutations in the age-1, and/or age-2 genes of C. elegans, that normally enhance life expectancy, can also increase resistance to killing by the bacterial pathogens Pseudomonas aeruginosa, Salmonella enterica var. Typhimurium, Burkholderia cepacia or Yersinia pseudotuberculosis. We also found that the rate at which wild-type C. elegans was killed by the bacterial pathogens tested increased as nematodes aged. In the case of P. aeruginosa infection, the difference in life span of wild type and age-1 mutants of C. elegans was not due to differences in the level of bacterial colonisation of the gut.