Decoration of Burkholderia Hcp1 protein to virus-like particles as a vaccine delivery platform.

Virus-like particles (VLPs) are protein-based nanoparticles frequently used as carriers in conjugate vaccine platforms. VLPs have been used to display foreign antigens for vaccination and to deliver immunotherapy against diseases. Hemolysin-coregulated proteins 1 (Hcp1) is a protein component of the Burkholderia type 6 secretion system, which participates in intracellular invasion and dissemination. This protein has been reported as a protective antigen and is used in multiple vaccine candidates with various platforms against melioidosis, a severe infectious disease caused by the intracellular pathogen Burkholderia pseudomallei. In this study, we used P22 VLPs as a surface platform for decoration with Hcp1 using chemical conjugation. C57BL/6 mice were intranasally immunized with three doses of either PBS, VLPs, or conjugated Hcp1-VLPs. Immunization with Hcp1-VLPs formulation induced Hcp1-specific IgG, IgG1, IgG2c, and IgA antibody responses. Furthermore, the serum from Hcp1-VLPs immunized mice enhanced the bacterial uptake and opsonophagocytosis by macrophages in the presence of complement. This study demonstrated an alternative strategy to develop a VLPs-based vaccine platform against Burkholderia species.

Identification and mechanism determination of the efflux pump subunit amrB gene mutations linked to gentamicin susceptibility in clinical Burkholderia pseudomallei from Malaysian Borneo.

The bacterium Burkholderia pseudomallei is typically resistant to gentamicin but rare susceptible strains have been isolated in certain regions, such as Thailand and Sarawak, Malaysia. Recently, several amino acid substitutions have been reported in the amrB gene (a subunit of the amrAB-oprA efflux pump gene) that confer gentamicin susceptibility. However, information regarding the mechanism of the substitutions conferring the susceptibility is lacking. To understand the mechanism of amino acid substitution that confers susceptibility, this study identifies the corresponding mutations in clinical gentamicin-susceptible B. pseudomallei isolates from the Malaysian Borneo (n = 46; Sarawak: 5; Sabah: 41). Three phenotypically confirmed gentamicin-susceptible (GENs) strains from Sarawak, Malaysia, were screened for mutations in the amrB gene using gene sequences of gentamicin-resistant (GENr) strains (QEH 56, QEH 57, QEH20, and QEH26) and publicly available sequences (AF072887.1 and BX571965.1) as the comparator. The effect of missense mutations on the stability of the AmrB protein was determined by calculating the average energy change value (ΔΔG). Mutagenesis analysis identified a polymorphism-associated mutation, g.1056 T > G, a possible susceptible-associated in-frame deletion, Delta V412, and a previously confirmed susceptible-associated amino acid substitution, T368R, in each of the three GENs isolates. The contribution of Delta V412 needs further confirmation by experimental mutagenesis analysis. The mechanism by which T368R confers susceptibility, as elucidated by in silico mutagenesis analysis using AmrB-modeled protein structures, is proposed to be due to the location of T368R in a highly conserved region, rather than destabilization of the AmrB protein structure.

Laboratory Safety: Handling Burkholderia pseudomallei Isolates without a Biosafety Cabinet.

Burkholderia pseudomallei is a tier 1 select agent that is associated with laboratory-acquired melioidosis, with international guidelines recommending isolate handling within a class II biosafety cabinet (BSC) in a biosafety level 3 (BSL3) facility. In low-resource settings, this may not be practical; therefore, we aimed to assess the risk of laboratory-acquired melioidosis during routine work. Prior exposure to the organism was determined with a questionnaire and concomitant serology. Of 30 laboratory scientists handling B. pseudomallei on 1,267 occasions outside a biosafety cabinet, no infections were documented and all participants remained seronegative. Additionally, we performed controlled environmental air sampling during 78 laboratory handling events, including plate opening, oxidase testing, and McFarland suspension creation. None of the experiments demonstrated aerosolization of the organism. This study suggests the risk of laboratory-acquired melioidosis is low. However, individual laboratories will need to undertake a risk assessment, including melioidosis endemicity, availability of resources for containment, the nature of routine handling to be undertaken, and the presence of predisposing risk factors for infection in the staff concerned. Additionally, laboratories should take region-specific guidelines into consideration. Further research is required to better inform on the overall risk of infection in the microbiology laboratory.

Optical microscopy reveals the dynamic nature of B. pseudomallei morphology during ß-lactam antimicrobial susceptibility testing.

BACKGROUND: In Gram-negative species, ß-lactam antibiotics target penicillin binding proteins (PBPs) resulting in morphological alterations of bacterial cells. Observations of antibiotic-induced cell morphology changes can rapidly and accurately differentiate drug susceptible from resistant bacterial strains; however, resistant cells do not always remain unchanged. Burkholderia pseudomallei is a Gram-negative, biothreat pathogen and the causative agent of melioidosis, an often fatal infectious disease for humans. RESULTS: Here, we identified ß-lactam targets in B. pseudomallei by in silico analysis. Ten genes encoding putative PBPs, including PBP-1, PBP-2, PBP-3 and PBP-6, were detected in the genomes of susceptible and resistant strains. Real-time, live-cell imaging of B. pseudomallei strains demonstrated dynamic morphological changes in broth containing clinically relevant ß-lactam antibiotics. At sub-inhibitory concentrations of ceftazidime (CAZ), amoxicillin-clavulanic acid (AMC), and imipenem (IPM), filamentation, varying in length and proportion, was an initial response of the multidrug-resistant strain Bp1651 in exponential phase. However, a dominant morphotype reemerged during stationary phase that resembled cells unexposed to antibiotics. Similar morphology dynamics were observed for AMC-resistant strains, MSHR1655 and 724644, when exposed to sub-inhibitory concentrations of AMC. For all B. pseudomallei strains evaluated, increased exposure time and exposure to increased concentrations of AMC at and above minimal inhibitory concentrations (MICs) in broth resulted in cell morphology shifts from filaments to spheroplasts and/or cell lysis. B. pseudomallei morphology changes were more consistent in IPM. Spheroplast formation followed by cell lysis was observed for all strains in broth containing IPM at concentrations greater than or equal to MICs, however, the time to cell lysis was variable. B. pseudomallei cell lengths were strain-, drug- and drug concentration-dependent. CONCLUSIONS: Both resistant and susceptible B. pseudomallei strains exhibited filamentation during early exposure to AMC and CAZ at concentrations used to interpret susceptibility (based on CLSI guidelines). While developing a rapid ß-lactam antimicrobial susceptibility test based on cell-shape alone requires more extensive analyses, optical microscopy detected B. pseudomallei growth attributes that lend insight into antibiotic response and antibacterial mechanisms of action.

Evaluation of a Rapid Diagnostic Test for Detection of Burkholderia pseudomallei in the Lao People's Democratic Republic.

Burkholderia pseudomallei causes significant global morbidity and mortality, with the highest disease burden in parts of Asia where culture-based diagnosis is often not available. We prospectively evaluated the Active Melioidosis Detect (AMD; InBios International, USA) lateral flow immunoassay (LFI) for rapid detection of B. pseudomallei in turbid blood cultures, pus, sputum, sterile fluid, urine, and sera. The performance of this test was compared to that of B. pseudomallei detection using monoclonal antibody latex agglutination (LA) and immunofluorescence assays (IFA), with culture as the gold standard. AMD was 99% (99/100; 95% confidence interval, 94.6 to 100%) sensitive and 100% (308/308; 98.8 to 100%) specific on turbid blood culture bottles, with no difference from LA or IFA. AMD specificity was 100% on pus (122/122; 97.0 to 100%), sputum (20/20; 83.2 to 100%), and sterile fluid (44/44; 92 to 100%). Sensitivity on these samples was as follows: pus, 47.1% (8/17; 23.0 to 72.2%); sputum, 33.3% (1/3; 0.84 to 90.6%); and sterile fluid, 0% (0/2; 0 to 84.2%). For urine samples, AMD had a positive predictive value of 94% (32/34; 79.7 to 98.5%) for diagnosing melioidosis in our cohort. AMD sensitivity on stored sera, collected prospectively from melioidosis cases during this study, was 13.9% (5/36; 4.7% to 29.5%) compared to blood culture samples taken on the same day. In conclusion, AMD is an excellent tool for rapid diagnosis of melioidosis from turbid blood cultures and maintains specificity across all sample types. It is a promising tool for urinary antigen detection, which could revolutionize diagnosis of melioidosis in resource-limited settings. Further work is required to improve sensitivity on nonblood culture samples.

Pulmonary Delivery of Ceftazidime for the Treatment of Melioidosis in a Murine Model.

Burkholderia pseudomallei, the etiological agent responsible for melioidosis, exhibits a great public health toll in its endemic regions. The elevation of B. pseudomallei to a Tier I select agent underscores the urgent need for effective therapeutics and preventatives. The current treatment regimen for melioidosis is suboptimal, requiring an intensive phase of intravenous antibiotic followed by months of oral antibiotics. Inhaled antibiotics are a promising avenue to pursue for pulmonary diseases, including melioidosis, since this mode of delivery mimics the likely exposure route and can provide high drug doses directly to the infected tissue. Ceftazidime was delivered via a nose-only system to BALB/c mice challenged with B. pseudomallei. Mice treated with nebulized ceftazidime became symptomatic but survived until study end, which was comparable to those treated intraperitoneally. Upon necropsy, bacteria remained within the spleens of the majority of the experimental animals. The effectiveness of nebulized ceftazidime warrants additional studies to improve the treatment regimen and to test as a prophylactic therapy against B. pseudomallei.

Factors affecting clinical outcomes in the management of melioidosis in Singapore: a 16-year case series.

BACKGROUND: Burkholderia pseudomallei is a gram negative bacteria that causes a spectrum of human diseases in the tropics. Although melioidosis is endemic in Southeast Asia, large clinical case series were rarely reported from metropolitan Singapore. METHODS: This is a retrospective study of 219 consecutive patients with culture proven infections due to Burkholderia pseudomallei between the years 2001 to 2016 managed in Singapore General Hospital (SGH). We aimed to review local patients' characteristics and identify clinical factors associated with mortality and recurrent melioidosis. RESULTS: Culture proven melioidosis occurred in 219 patients, 83.1% were male with a mean age of 55.7 ± 14.3 years and 63.0% had diabetes mellitus. Most patients (71.7%) present within 4 weeks of symptom onset and the most common symptom was fever. The majority of patients had bacteremia (67.6%) and had infection involving the respiratory system (71.2%), presenting most frequently with multi-lobar pneumonia. Thirty-four (15.5%) deaths occurred during the initial hospitalisation with a median time from presentation to death of 6.0 days (interquartile range: 2.8-16.3). Twelve patients demised before the diagnosis of melioidosis was made. Univariate analysis identified patients with symptom duration of longer than 4 weeks, bacteremia, and disease requiring mechanical ventilation, inotropic support or temporary dialysis as factors that were significantly associated with mortality. Having bacteremia and disease requiring mechanical ventilation remained statistically significant factors in the multivariable analysis. Twenty-one (11.4%) patients developed at least 1 episode of culture proven recurrent infection, with 15 recurring within the first 12 months of their initial infection. Eight patients developed more than 1 episode of culture proven recurrent infection. Patients with multifocal infection were more likely to develop recurrent infection. CONCLUSION: In metropolitan Singapore, melioidosis was associated with mortality in excess of 15%, where more than a third occurred before diagnosis. This study reminds local physicians that melioidosis is still a serious infection affecting local male diabetic patients and an important differential diagnosis in a patient presenting with severe multi-lobar pneumonia and septic shock. Recurrent infections occurred in 11.4% and the weight-based dosing of oral eradication antibiotics may improve the management of this disease locally.

Burkholderia pseudomallei induces IL-23 production in primary human monocytes.

Burkholderia pseudomallei, a gram-negative intracellular bacterium, is a causative agent of melioidosis. The bacterium has been shown to induce the innate immune response, particularly pro-inflammatory cytokine production in several of both mouse and human cell types. In the present study, we investigate host immune response in B. pseudomallei-infected primary human monocytes. We discover that wild-type B. pseudomallei is able to survive and multiply inside the primary human monocytes. In contrast, B. pseudomallei LPS mutant, a less virulent strain, is susceptible to host killing during bacterial infection. Moreover, microarray result showed that wild-type B. pseudomallei but not B. pseudomallei LPS mutant is able to activate gene expression of IL-23 as demonstrated by the up-regulation of p19 and p40 subunit expression. Consistent with gene expression analysis, the secretion of IL-23 analyzed by ELISA also showed that wild-type B. pseudomallei induces a significantly higher level of IL-23 secretion than that of B. pseudomallei LPS mutant. These results implied that IL-23 may be an important cytokine for the innate immune response during B. pseudomallei infection. The regulation of IL-23 production may drive the different host innate immune responses between patients and may relate to the severity of melioidosis.

The epidemiology and clinical spectrum of melioidosis in a teaching hospital in a North-Eastern state of Malaysia: a fifteen-year review.

BACKGROUND: Over the last two decades, many epidemiological studies were performed to describe risks and clinical presentations of melioidosis in endemic countries. METHODS: We performed a retrospective analysis of 158 confirmed cases of melioidosis collected from medical records from 2001 to 2015 in Hospital Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia, in order to update the current status of melioidosis clinical epidemiology in this putatively high risk region of the country. RESULTS: Principal presentations in patients were lung infection in 65 (41.1 %), skin infection in 44 (27.8 %), septic arthritis/osteomyelitis in 20 (12.7 %) and liver infection in 19 (12.0 %). Bacteremic melioidosis was seen in most of patients (n = 121, 76.6 %). Focal melioidosis was seen in 124 (78.5 %) of patients and multi-focal melioidosis was reported in 45 (28.5 %) cases. Melioidosis with no evident focus was in 34 (21.5 %) patients. Fifty-four (34.2 %) patients developed septic shock. Internal organ abscesses and secondary foci in lungs and/or soft tissue were common. A total of 67 (41 %) cases presented during the monsoonal wet season. Death due to melioidosis was reported in 52 (32.9 %) patients, while relapses were occurred in 11 (7.0 %). Twelve fatal melioidosis cases seen in this study were directly attributed to the absence of prompt acute-phase treatment. Predisposing risk factors were reported in most of patients (n = 133, 84.2 %) and included diabetes (74.7 %), immune disturbances (9.5 %), cancer (4.4 %) and chronic kidney disease (11.4 %). On multivariate analysis, the only independent predictors of mortality were the presence of at least one co-morbid factor (OR 3.0; 95 % CI 1.1-8.4), the happening of septic shock (OR 16.5; 95 % CI 6.1-44.9) and age > 40 years (OR 6.47; 95 % CI 1.7-23.8). CONCLUSIONS: Melioidosis should be recognized as an opportunistic nonfatal infection for healthy person. Prompt early diagnosis and appropriate antibiotics administration and critical care help in improved management and minimizing risks for death.

Assessing the national antibiotic surveillance data to identify burden for melioidosis in Malaysia.

Objectives: A leading cause of morbidity and mortality in Southeast Asia, the epidemiological data on melioidosis disease occurrence and mortality in Malaysia is not comprehensive. The aim of this study is to determine the burden of melioidosis and assess the National Surveillance for Antibiotic Resistance (NSAR) data as a potential tool melioidosis surveilance in Malaysia. Methods: We performed a retrospective analysis on the B. pseudomallei reposited data submitted to the NSAR network between January 2014 and December 2020. The data were screened for information on patient demographics and specimen types. Additional patient comorbidities and outcomes were drawn from parallel surveillance for bacteremic melioidosis. Results: The average annual incidence rate of melioidosis between 2014-2020 was 3.41 per 100,000 population and was significantly different between states (P <0.001). The highest incidence was observed in Pahang at 11.33 per 100,000 population. Individuals of Malay ethnicity, from the states of Pahang, Johor, Perak, and Negeri Sembilan aged 40-49, who were diabetic and working in agriculture-related sectors had a higher risk of succumbing to the infection. Conclusion: Assessing the NSAR data proved to be a useful tool for the determination of the incidence and socio-demographic risk factors attributed to melioidosis in Malaysia.

Effect of O antigen glycosyl isomerase gene mutation on biological property and pathogenicity of Burkholderia pseudomallei strain BPC006.

Burkholderia pseudomallei, an intracellular pathogen, is responsible for melioidosis, a zoonotic disease. Its pathogenesis involves several virulence factors, among which lipopolysaccharide (LPS) plays a crucial role. Our research reveals that the O antigen present within the LPS significantly regulates the host immune response. In a previous study, we obtained a B. pseudomallei mutant strain ΔwbiI. Here, the purification of LPS from ΔwbiI and a gas chromatography-mass spectrometry (GC-MS) analysis were conducted. The results confirmed the absence of specific sugar 6-deoxy-Talp, which is a typical component of the O antigen in the wild type B. pseudomallei. Our findings underscore the potent impact the O antigen exerts on the virulence of B. pseudomallei. The ΔwbiI strain displayed significantly increased invasiveness and cytotoxicity in vitro. This enhanced cytotoxicity seems to be related to the exposure of lipid A and an increased cell membrane hydrophobicity resulting from the deletion of the O antigen. Additionally, in mouse models, the ΔwbiI strain resulted in a heightened host lethality and an excessive inflammatory response in mice. These findings indicate that the O-antigenic polysaccharide moiety of B. pseudomallei plays a role in its pathogenicity in vitro and in vivo.

Management of unexpected laboratory exposure to Burkholderia pseudomallei.

Burkholderia pseudomallei is a Gram-negative saprophytic bacillus that causes melioidosis. The infection is endemic in South-East of Asia and Northern Australia. B. pseudomallei has been designated as bioterrorism agent and its manipulation should be done in a biological safety level 3 capability. Workers in laboratories may be accidentally exposed to B. pseudomallei before its identification, with a risk of laboratory-acquired melioidosis. We want to describe a case of melioidosis occurred in our hospital and its management at laboratory. The objective of this article is to provide guidance to microbiologists confronted with a suspicious case of B. pseudomallei on the management of the exposition. We report here a couple of microbiological arguments that can usually guide microbiologists towards presumptive identification of B. pseudomallei. This case report shows the importance of MALDI-TOF MS accurate databases to ensure accurate microbial identification and antibiotic prophylaxis adapted to individuals who were exposed. We also want to underline the importance of developing an effective strategy of prevention against any accidental exposure that can occur in a microbiological laboratory.

Characterization of Burkholderia pseudomallei O antigens in different clinical strains.

O antigen is the major component of lipopolysaccharide LPS. The chemical structure of the O antigen determines the LPS serospecificity of the bacteria, and the diversity of O antigen is the basis for serotyping Burkholderia pseudomallei. In this study, structural elucidation of type B O antigen obtained from a clinical B. pseudomallei strain was conducted, and the effects of different types of LPS on macrophage differentiation were investigated. The O antigen was found to be composed of repeating units of [→4)-α-L-Rhap(1 â†’ 4)-α-L-Rhap(1→2)-α-L-Rhap(1 â†’ 2)-α-L-Rhap(1 â†’ 3)-α-L-Rhap(1 â†’ 3)-α-L-Rhap(1 â†’ 4)-α-L-Rhap(1 â†’ 6)-α-D-Galp(1→]n, where some of the →4)-α-L-Rhap(1 â†’ units were substituted at O-3 by ß-D-Xylp(1 â†’ residues, and minor →3)-α-L-Rhap(1 â†’ units were substituted at O-2 by ß-D-Xylp(1 â†’ residues. Meahwhile, the →6)-α-D-Galp(1 â†’ units were substituted at O-3 by α-D-Galp(1 â†’ residues. Furthermore, both type A and type B O antigens of B. pseudomallei could polarize macrophages toward the M1 phenotype, but the core oligosaccharides had no such activity. Therefore, we deduced that this polarization relies on the O antigen of LPS and might be related to the ability of B. pseudomallei to survive and replicate within macrophages. Thus, the characterization of different types of O antigen structural motifs is essential for further clarifying the persistence/survival mechanisms and inflammatory potential of B. pseudomallei.

Genomics and structural insight into the masking of gentamicin-resistance in clinical Burkholderia pseudomallei strain VB29710 from India.

The present study reported a rare gentamicin-susceptible ß-lactamase (PenA, OXA-57) expressing clinical Burkholderia pseudomallei isolate VB29710 from India. Whole-genome sequencing and structural analyses revealed the insertion of R962 and L963 into AmrB, the transmembrane-protein of the AmrAB-OprA efflux-pump that affected aminoglycoside-efflux through local alterations in backbone conformation.

Melioidosis as a Mystique Infection: A Study From Central India.

INTRODUCTION: Melioidosis is caused by the Gram-negative bacilli Burkholderia pseudomallei, which is found in contaminated water and soil and spreads via inhalation, inoculation, and ingestion. Melioidosis manifests diversely in immunocompetent and immunocompromised patients, ranging from asymptomatic to life-threatening respiratory distress, septic shock, localized tissue infection, necrotizing pneumonia, and soft organ abscesses.  Methods: An 18-month observational study was conducted at a tertiary center in central India among various confirmed melioidosis cases, with data gathered and analyzed. Aerobic culture and sensitivity were performed in all studied cases, either in blood/body fluid/localized collection - using blood agar media for the culture and disc diffusion method on Mueller Hinton agar for sensitivity. Other tests, such as radiological imaging, were conducted according to symptoms and signs of localized infection. RESULTS: The melioidosis cases under study were compared on various clinical/presenting parameters. Melioidosis has a variety of risk factors, but we found that, in India, diabetic patients are at a higher risk of this infection, particularly fatal forms, as all of the patients in our study were diabetic. Melioidosis is known to have joint involvement, either as a source of infection or later in the course of the disease. All cases were successfully treated with antibiotics and surgical procedures, demonstrating the significance of determining disease etiology, early diagnosis, and rapid early management. CONCLUSION:  Melioidosis is a potentially fatal disease, particularly in diabetics, with a wide range of symptoms and complications. Physicians face a variety of challenges, including clinical symptoms resembling other chronic illnesses, such as tuberculosis, delays in laboratory confirmation, underdiagnosis, reduced reporting, and a lack of suspicion. Because there are very little data and it is a seldom reported infection from central India, we are publishing a study on seven melioidosis patients.

Burkholderia pseudomallei BicA protein promotes pathogenicity in macrophages by regulating invasion, intracellular survival, and virulence.

Burkholderia pseudomallei (Bpm) is the causative agent of melioidosis disease. Bpm is a facultative intracellular pathogen with a complex life cycle inside host cells. Pathogenic success depends on a variety of virulence factors with one of the most critical being the type 6 secretion system (T6SS). Bpm uses the T6SS to move into neighboring cells, resulting in multinucleated giant cell (MNGC) formation, a strategy used to disseminate from cell to cell. Our prior study using a dual RNA-seq analysis to dissect T6SS-mediated virulence on intestinal epithelial cells identified BicA as a factor upregulated in a T6SS mutant. BicA regulates both type 3 secretion system (T3SS) and T6SSs; however, the extent of its involvement during disease progression is unclear. To fully dissect the role of BicA during systemic infection, we used two macrophage cell lines paired with a pulmonary in vivo challenge murine model. We found that ΔbicA has a distinct intracellular replication defect in both immortalized and primary macrophages, which begins as early as 1 h post-infection. This intracellular defect is linked with the lack of cell-to-cell dissemination and MNGC formation as well as a defect in T3SS expression. The in vitro phenotype translated in vivo as ΔbicA was attenuated in a pulmonary model of infection, demonstrating a distinct macrophage activation profile and a lack of pathological features present in the wild type. Overall, these results highlight the role of BicA in regulating intracellular virulence and demonstrate that specific regulation of secretion systems has a significant effect on host response and Bpm pathogenesis. IMPORTANCE Melioidosis is an understudied tropical disease that still results in ~50% fatalities in infected patients. It is caused by the Gram-negative bacillus Burkholderia pseudomallei (Bpm). Bpm is an intracellular pathogen that disseminates from the infected cell to target organs, causing disseminated disease. The regulation of secretion systems involved in entry and cell-to-cell spread is poorly understood. In this work, we characterize the role of BicA as a regulator of secretion systems during infection of macrophages in vitro and in vivo. Understanding how these virulence factors are controlled will help us determine their influence on the host cells and define the macrophage responses associated with bacterial clearance.

Phenotypic and genetic alterations of Burkholderia pseudomallei in patients during relapse and persistent infections.

The bacterium Burkholderia pseudomallei is the causative agent of melioidosis, a severe tropical disease associated with high mortality and relapse and persistent infections. Treatment of melioidosis requires prolonged antibiotic therapy; however, little is known about relapse and persistent infections, particularly the phenotypic and genetic alterations of B. pseudomallei in patients. In this study, we performed pulsed-field gel electrophoresis (PFGE) to compare the bacterial genotype between the initial isolate and the subsequent isolate from each of 23 suspected recurrent and persistent melioidosis patients in Northeast Thailand. We used whole-genome sequencing (WGS) to investigate multilocus sequence types and genetic alterations of within-host strain pairs. We also investigated the bacterial phenotypes associated with relapse and persistent infections, including multinucleated giant cell (MNGC) formation efficiency and intracellular multiplication. We first identified 13 (1.2%) relapse, 7 (0.7%) persistent, and 3 (0.3%) reinfection patients from 1,046 survivors. Each of the 20 within-host strain pairs from patients with relapse and persistent infections shared the same genotype, suggesting that the subsequent isolates arise from the infecting isolate. Logistic regression analysis of clinical data revealed regimen and duration of oral antibiotic therapies as risk factors associated with relapse and persistent infections. WGS analysis demonstrated 17 within-host genetic alteration events in 6 of 20 paired isolates, including a relatively large deletion and 16 single-nucleotide polymorphism (stocktickerSNP) mutations distributed across 12 genes. In 1 of 20 paired isolates, we observed significantly increased cell-to-cell fusion and intracellular replication in the second isolate compared with the initial isolate from a patient with persistent infection. WGS analysis suggested that a non-synonymous mutation in the tssB-5 gene, which encoded an essential component of the type VI secretion system, may be associated with the increased intracellular replication and MNGC formation efficiency of the second isolate of the patient. This information provides insights into genetic and phenotypic alterations in B. pseudomallei in human melioidosis, which may represent a bacterial strategy for persistent and relapse infections.

Identification of candidate blood biomarkers for the diagnosis of septicaemic melioidosis based on WGCNA.

Melioidosis is an infectious disease caused by Burkholderia pseudomallei (Bp), a gram-negative bacillus. Sepsis is the most prevalent type of melioidosis. Due to factors such as lack of precision and slow presentation of bacterial culture tests, the misdiagnosis rate could exceed 100 per cent. Therefore, more reliable, and adaptable diagnostic methods are urgently needed. Weighted gene co-expression network analysis (WGCNA) was employed to screen the featured modules specially expressed in sepsis patients caused by Bp. Two representative co-expression modules were selected to perform gene ontology(GO) and KEGG analysis using ClusterProfiler package based on R language. We found that antigen processing and presentation of exogenous peptide antigen via MHC class I pathway, cytosol to ER transport and cell killing related pathways enriched in darkmagenta module which significantly correlated with the sepsis caused by Bp. Eventually, a diagnostic 6-mRNA signature consisting of ASPHD2, LAP3, SEPT4, FAM26F, WARS and LGALS3BP was identified, which could discern the sepsis caused by Bp compared with other organisms. This will provide a new insight in screening markers for early detection of sepsis caused by Bp, and the interaction between pathogens and hosts. This should shed light on the early detection of Bp-caused infectious diseases.

Biochemical, structural, and computational studies of a γ-carbonic anhydrase from the pathogenic bacterium Burkholderia pseudomallei.

Melioidosis is a severe disease caused by the highly pathogenic gram-negative bacterium Burkholderia pseudomallei. Several studies have highlighted the broad resistance of this pathogen to many antibiotics and pointed out the pivotal importance of improving the pharmacological arsenal against it. Since γ-carbonic anhydrases (γ-CAs) have been recently introduced as potential and novel antibacterial drug targets, in this paper, we report a detailed characterization of BpsγCA, a γ-CA from B. pseudomallei by a multidisciplinary approach. In particular, the enzyme was recombinantly produced and biochemically characterized. Its catalytic activity at different pH values was measured, the crystal structure was determined and theoretical pKa calculations were carried out. Results provided a snapshot of the enzyme active site and dissected the role of residues involved in the catalytic mechanism and ligand recognition. These findings are an important starting point for developing new anti-melioidosis drugs targeting BpsγCA.

BipD of Burkholderia pseudomallei: Structure, Functions, and Detection Methods.

Melioidosis is a severe disease caused by Burkholderia pseudomallei (B. pseudomallei), a Gram-negative environmental bacterium. It is endemic in Southeast Asia and Northern Australia, but it is underreported in many other countries. The principal routes of entry for B. pseudomallei are skin penetration, inhalation, and ingestion. It mainly affects immunocompromised populations, especially patients with type 2 diabetes mellitus. The laboratory diagnosis of melioidosis is challenging due to its non-specific clinical manifestations, which mimic other severe infections. The culture method is considered an imperfect gold standard for the diagnosis of melioidosis due to its low sensitivity. Antibody detection has low sensitivity and specificity due to the high seropositivity among healthy people in endemic regions. Antigen detection using various proteins has been tested for the rapid determination of B. pseudomallei; however, it presents certain limitations in terms of its sensitivity and specificity. Therefore, this review aims to frame the present knowledge of a potential target known as the Burkholderia invasion protein D (BipD), including future directions for its detection using an aptamer-based sensor (aptasensor).