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Burkholderia arboris bacteremia initially identified as Burkholderia cepacia complex: a genome-based case report.

We report a bloodstream Burkholderia arboris isolate from a 75-year-old man without cystic fibrosis. The organism was recovered from both aerobic bottles of two separately collected blood-culture sets and was initially assigned to the Burkholderia cepacia complex (Bcc) by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Whole-genome sequencing yielded three circular chromosomes and one circular plasmid. DFAST_QC identified B. arboris as the only type-strain match above the species threshold, with an average nucleotide identity of 99.48%; the next-highest match was B. seminalis at 93.33%. Multilocus sequence typing identified ST-2575, and ResFinder detected no acquired antimicrobial resistance genes. The patient improved after 14 days of meropenem therapy without recurrent B. arboris bacteremia. This report adds a clinically supported bloodstream infection, a complete genome resource, and detailed susceptibility data, while illustrating the importance of up-to-date reference genomes for species-level interpretation of unusual Bcc isolates.

Humans

The Burkholderia cepacia epidemic strain marker is part of a novel genomic island encoding both virulence and metabolism-associated genes in Burkholderia cenocepacia.

The Burkholderia cepacia epidemic strain marker (BCESM) is a useful epidemiological marker for virulent B. cenocepacia strains that infect patients with cystic fibrosis. However, there was no evidence that the original marker, identified by random amplified polymorphic DNA fingerprinting, contributed to pathogenicity. Here we demonstrate that the BCESM is part of a novel genomic island encoding genes linked to both virulence and metabolism. The BCESM was present on a 31.7-kb low-GC-content island that encoded 35 predicted coding sequences (CDSs): an N-acyl homoserine lactone (AHL) synthase gene (cciI) and corresponding transcriptional regulator (cciR), representing the first time cell signaling genes have been found on a genomic island; fatty acid biosynthesis genes; an IS66 family transposase; transcriptional regulator CDSs; amino acid metabolism genes; and a group of hypothetical genes. Mutagenesis of the AHL synthase, amidase (amiI), and porin (opcI) genes on the island was carried out. Testing of the isogenic mutants in a rat model of chronic lung infection demonstrated that the amidase played a role in persistence, while the AHL synthase and porin were both involved in virulence. The island, designated the B. cenocepacia island (cci), is the first genomic island to be defined in the B. cepacia complex and its discovery validates the original epidemiological correlation of the BCESM with virulent CF strains. The features of the cci, which overlap both pathogenicity and metabolism, expand the concept of bacterial pathogenicity islands and illustrate the diversity of accessory functions that can be acquired by lateral gene transfer in bacteria.

Amidohydrolases

Quorum sensing and DNA methylation play active roles in clinical Burkholderia phase variation.

Phenotypic diversity in bacteria often results from adaptation to changing environmental conditions, exemplified by variable colony morphotypes. In Burkholderia pseudomallei, discrete genomic alterations and modulation of gene expression facilitate adaptation. Adapted variants of species within the Burkholderia cepacia complex (Bcc) often lose the pC3 virulence megaplasmid, impacting their colony morphology and their production of virulence factors. In this study, we characterize variants arising in Burkholderia ambifaria clinical isolates using proteomics and phenotypic tests and show that some of them have retained the pC3, indicating a distinct phase variation mechanism at play in this Bcc species. Interestingly, variants of B. ambifaria strains CEP0996 (pC3-null) and HSJ1 (pC3-positive) still share similarities in phenotypes controlled by the Cep quorum-sensing (QS) system. We further investigated the role of QS in B. ambifaria HSJ1 phase variation and confirmed that the Cep QS system is important for the emergence of variants. Given that DNA methylation is a key epigenetic factor regulating virulence factors in Burkholderia cenocepacia, we hypothesized that adenosine DNA methylation also governs phase variation in B. ambifaria HSJ1. By deleting the genes encoding putative adenosine DNA methyltransferases, we discovered that an orphan type II DNA methyltransferase inhibits the emergence of phase variants. This study is the first to demonstrate that quorum sensing and adenosine DNA methylation are two antagonistic systems independently controlling phase variation in B. ambifaria.IMPORTANCESome Burkholderia species are pathogenic to plants, animals, or humans. In immunocompromised individuals, and people suffering from cystic fibrosis, infection from the Burkholderia cepacia complex (Bcc) can lead to "cepacia syndrome." In northern Australia and southeast Asia, melioidosis caused by Burkholderia pseudomallei is prevalent among native population, particularly among people with diabetes, chronic lung or kidney disease or alcoholism. Burkholderia's phenotypic plasticity, including colony morphotype variation (CMV), enables rapid adaptation to diverse environments, enhancing its survival and pathogenicity. This study reveals phase variation as a new CMV mechanism within the Bcc group and is the first to report that quorum sensing and DNA methylation are involved in phase variation. Understanding the underlying mechanisms of CMV could lead to the development of targeted therapies against these highly antibiotic-tolerant bacteria.

Quorum Sensing

Exploring phage-host interactions in Burkholderia cepacia complex bacterium to reveal host factors and phage resistance genes using CRISPRi functional genomics and transcriptomics.

Complex interactions of bacteriophages with their bacterial hosts determine phage host range and infectivity. While phage defense systems and host factors have been identified in model bacteria, they remain challenging to predict in non-model bacteria. In this paper, we integrate functional genomics and transcriptomics to investigate phage-host interactions, revealing active phage resistance and host factor genes in Burkholderia cenocepacia K56-2. Burkholderia cepacia complex species are commonly found in soil and are opportunistic pathogens in immunocompromised patients. We studied infection of B. cenocepacia K56-2 with Bcep176, a temperate phage isolated from Burkholderia multivorans. A genome-wide dCas9 knockdown library targeting B. cenocepacia K56-2 was constructed, and a pooled infection experiment identified 63 novel genes or operons coding for candidate host factors or phage resistance genes. The activities of a subset of candidate host factor and resistance genes were validated via single-gene knockdowns. Transcriptomics of B. cenocepacia K56-2 during Bcep176 infection revealed that expression of genes coding for host factor and resistance candidates identified in this screen was significantly altered during infection by 4 h post-infection. Identifying which bacterial genes are involved in phage infection is important to understand the ecological niches of B. cenocepacia and its phages, and for designing phage therapies.IMPORTANCEBurkholderia cepacia complex bacteria are opportunistic pathogens inherently resistant to antibiotics, and phage therapy is a promising alternative treatment for chronically infected patients. Burkholderia bacteria are also ubiquitous in soil microbiomes. To develop improved phage therapies for pathogenic Burkholderia bacteria, or engineer phages for applications, such as microbiome editing, it's essential to know the bacterial host factors required by the phage to kill bacteria, as well as how the bacteria prevent phage infection. This work identified 65 genes involved in phage-host interactions in Burkholderia cenocepacia K56-2 and tracked their expression during infection. These findings establish a knowledge base to select and engineer phages infecting or transducing Burkholderia bacteria.

Bacteriophages

Whole genome study and construction of SHERLOCK detection method for endemic strains of Burkholderia pseudomallei in Hainan based on third-generation sequencing.

UNLABELLED: Burkholderia pseudomallei (Bp) is a gram-negative bacterium found in soil and surface water. It is also the pathogen that causes melioidosis disease in humans and animals. This study aimed to obtain the whole genome sequence of the endemic strain of Bp in Hainan, using third-generation sequencing (TGS) technology, and elucidate the genome structure, function, and genetic evolution. Additionally, the study aimed to achieve rapid and specific identification of these endemic strains using specific high-sensitivity enzymatic reporter unlocking (SHERLOCK) detection technology, providing a new strategy for the early diagnosis of melioidosis. Utilizing the PacBio platform for TGS technology, we completed whole genome sequencing of 16 Bp strains from Hainan. High-precision and complete genome sequences were obtained through quality control and genome assembly of the sequencing data. Additionally, we established a nucleic acid detection technology platform based on SHERLOCK, which could be completed from nucleic acid extraction to result reading within 1-2 hours, demonstrating good sensitivity and specificity (both are 100%). The lateral chromatography strip method does not require special equipment and holds promise as an immediate screening method for the early diagnosis of melioidosis. IMPORTANCE: Melioidosis is a highly pathogenic infectious disease caused by a gram-negative bacterium of Burkholderia pseudomallei (Bp). The traditional gold standard for diagnosing melioidosis is still isolation and culture from clinical samples. Although this method has high specificity, it has low sensitivity and is time-consuming, which often leads to misdiagnosis or missed diagnosis of melioidosis, affecting subsequent treatment. In this study, recombinase polymerase amplification technology and clustered regularly interspaced short palindromic repeats/Cas13a technology were combined to establish the Specific High-sensitivity Enzymatic Reporter Unlocking detection technology, which can achieve rapid and accurate identification of Bp, providing a new method for the early diagnosis of melioidosis.

Burkholderia pseudomallei

Metagenome-based diversity and functional analysis of culturable microbes in sugarcane.

UNLABELLED: Sugarcane is a key crop for sugar and energy production, and understanding the diversity of its associated microbes is crucial for optimizing its growth and health. However, there is a lack of thorough investigation and use of microbial resources in sugarcane. This study conducted a comprehensive analysis of culturable microbes and their functional features in different tissues and rhizosphere soil of four diverse sugarcane species using metagenomics techniques. The results revealed significant microbial diversity in sugarcane's tissues and rhizosphere soil, including several important biomarker bacterial taxa identified, which are reported to engage in several processes that support plant growth, such as nitrogen fixation, phosphate solubilization, and the production of plant hormones. The Linear discriminant analysis Effect Size (LEfSe) studies identified unique microbial communities in different parts of the same sugarcane species, particularly Burkholderia, which exhibited significant variations across the sugarcane species. Microbial analysis of carbohydrate-active enzymes (CAZymes) indicated that genes related to sucrose metabolism were mostly present in specific bacterial taxa, including Burkholderia, Pseudomonas, Paraburkholderia, and Chryseobacterium. This study improves understanding of the diversities and functions of endophytes and rhizosphere soil microbes in sugarcane. Moreover, the approaches and findings of this study provide valuable insights for microbiome research and the use of comparable technologies in other agricultural fields. IMPORTANCE: This work utilized metagenomics techniques for conducting a comprehensive examination of culturable microbes and their functional characteristics in various tissues and rhizosphere soil of four distinct sugarcane species. This study enhances comprehension of the diversity and functions of endophytes and rhizosphere soil microbes in sugarcane. Furthermore, the methodologies and discoveries of this work offer new perspectives for microbiome investigation and the use of similar technologies in other agricultural fields.

Saccharum

Comparative genomics approaches to identify genomic regions associated with the antimicrobial activity of Pseudomonas protegens PBL3.

The environmental bacterium Pseudomonas protegens PBL3 has antagonistic activity against the plant pathogenic bacterium Burkholderia glumae, an important pathogen in rice. The antimicrobial activity of P. protegens PBL3 was found in the bacteria-free secreted fraction (secretome), but the specific molecules, as well as the genetic basis of that activity, have not been identified. In this study, we integrated genomic information with antimicrobial assays on P. protegens PBL3 and additional six Pseudomonas spp. strains, to identify putative genomic regions in P. protegens PBL3 associated with antimicrobial activity. We hypothesized that Pseudomonas spp. strains with antimicrobial activity against B. glumae have conserved genes with P. protegens PBL3 that are absent in strains lacking activity. Comparative genomics analyses with anvi'o and progressiveMauve, and using P. protegens PBL3 as the reference genome, revealed 188 genes uniquely present in antimicrobial-producing strains. Seven of those genes were annotated as biosynthetic gene clusters predicted to encode secondary metabolites; additional genes were grouped into 25 contiguous clusters with functions annotated as secretion, signal transduction, regulation, transport/efflux, carbohydrate metabolism and one with an additional uncharacterized function. Altogether, this study uncovered a complex and multi-functional network of candidate genes, suggesting that the antimicrobial activity in P. protegens PBL3 is not limited to biosynthetic pathways but also involves additional regulatory, metabolic and export modules to synthesize and deploy antimicrobials.

Pseudomonas

Proteomic-based identification of novel EV-derived protein antibodies biomarkers for melioidosis diagnosis.

Melioidosis, caused by Burkholderia pseudomallei (Bp), is a life-threatening disease characterized by diverse clinical manifestations and limited diagnostic capabilities. Extracellular vesicles (EVs) have emerged as critical carriers of novel antibody targets for serodiagnosis. In this study, we established a Bp-infected BEAS-2B cell model (Bp/BEAS-2B) and isolated EV from both Bp and Bp/BEAS-2B cells to generate EV proteome, identifying potential antigenic biomarkers for melioidosis diagnosis. Bioinformatics analysis identified PPEP and POMCR proteins as candidate antigens, with BLF1 and omp A serving as positive controls. Using a self-developed IgM-ELISA, serum samples from 43 melioidosis patients and 47 healthy volunteers were analyzed to detect antibodies against these antigens. Anti-POMCR IgM demonstrated exceptional diagnostic performance, with an AUC of 0.9872 (95% CI: 0.9713-1.003), sensitivity of 93.02% and specificity of 97.92% at a cutoff value of OD450 = 0.118. Similarly, IgM against PPEP, BLF1, and omp A also showed high diagnostic accuracy, with AUC values of 0.969, 0.9621, and 0.976, respectively. The accuracy of anti-POMCR and anti-PPEP were 96.43% and 95.54%, respectively, equivalent to anti-omp A (93.75%) and anti-BLF1 (91.96%). Antibodies to EV-derived proteins effectively differentiated melioidosis patients from other bacterial infections and healthy volunteers, highlighting their clinical potential as diagnostic tools for melioidosis.

Humans

Effects of a novel Paraburkholderia phage IPK on the phenanthrene degradation efficiency of the PAH-degrading strain Paraburkholderia caledonica Bk.

Phages are a major cause of bacterial mortality, affecting bacterial diversity and ecosystem functioning. However, the impact of phage-host interactions in contaminated environments and their role in pollutant biodegradation have largely been overlooked. We isolated and characterized a novel phage that infects the PAH-degrading bacterium Paraburkholderia caledonica Bk from a polycyclic aromatic hydrocarbon (PAH)-contaminated soil and investigated the effect of different multiplicity of infection (MOI) ratios on the degradation efficiency of phenanthrene. The phage IPK is a temperate phage with a wide pH and temperature tolerance and a burst size of 80  PFU ml⁻1. The phage was classified as a member of the Caudoviricetes and is related to Pseudomonas and Burkholderia phages. However, its low intergenomic similarity indicates that it is a new species. Three auxiliary metabolic genes (AMGs) related to amino acid metabolism and to bacterial growth regulation were identified in the phage genome. The highest multiplicity of infection (MOI 10) showed a rapid recovery of the host density and greater phenanthrene degradation than MOIs ranging from 0.01 to 1. This work highlights the important role of phage-host interactions in modulating the efficiency of pollutant degradation, which could be a key for improving the establishment of inoculants in bioremediation processes.

Phenanthrenes

Recurrent and unusual infections unmasking a rare inborn error of immunity: a case report RAS-associated Autoimmune Lymphoproliferative Disease (RALD).

BACKGROUND: RAS-associated Autoimmune Lymphoproliferative Disease (RALD) is a rare, non-malignant lymphoproliferative disorder caused by somatic mutations in RAS genes that impair lymphocyte apoptosis. Patients often present with features of lymphoproliferation, autoimmune manifestations, and an increased risk of malignant transformation. CASE PRESENTATION: We report the case of a 3-year-old boy with splenic microabscesses and Burkholderia pseudomallei IgM serology positivity, who was treated as melioidosis. He had recurrent respiratory infections and chronic rhinorrhoea since the age of one year. Clinical examination revealed persistent lymphadenopathy and hepatosplenomegaly. Laboratory investigations demonstrated persistent absolute monocytosis and thrombocytopenia, while immunological evaluation showed elevated IgM levels and B-cell lymphocytosis. Whole exome sequencing identified a heterozygous pathogenic variant in NRAS, NM_002524.5:c.35G > C, NP_002515.1:p.Gly12Ala, establishing the diagnosis of RALD. The patient was subsequently started on antibiotic prophylaxis and immunoglobulin replacement therapy, and his family was counseled regarding the potential role of immunosuppressive therapy and hematopoietic stem cell transplantation (HSCT) in future management. CONCLUSIONS: This case highlights the coexistence of an unusual infection with a rare inborn error of immunity, expanding the recognized infectious spectrum of RALD. It underscores the importance of considering RALD in patients presenting with recurrent or atypical infections and persistent lymphoproliferative features. Early recognition and molecular genetic testing are essential for confirming the diagnosis and guiding individualized management.

Humans