Molecular approaches to pathogenesis study of Burkholderia cenocepacia, an important cystic fibrosis opportunistic bacterium

The mntH gene of Burkholderia cenocepacia influences motility and quorum sensing to control virulence

Quorum sensing (QS) signals widely exist in bacteria to control biological functions in response to populations of cells. Burkholderia cenocepacia, an important opportunistic pathogen in patients with cystic fibrosis (CF), is commonly found in the environment and mostly utilizes the N-acylhomoserine lactone (AHL) and cis-2-dodecenoic acid (BDSF) QS systems to control biological functions. Our previous study illuminated the detailed mechanism by which B.cenocepacia integrates BDSF and cyclic diguanosine monophosphate (c-di-GMP) signals to control virulence. Here, we employed Tn5 transposon mutagenesis to identify genes related to the BDSF QS system. One of the most significantly attenuated mutants had an insertion in the mntH gene. Here, we showed that MntH (Bcam0836), a manganese transport protein, controls QS-regulated phenotypes, including motility, biofilm formation and virulence. We also found that. BDSF production was attenuated at both the gene and signaling levels in the Bcam0836 mutant, and that Bcam0836 influenced the expression of some genes regulated by the BDSF receptor RpfR and the downstream regulator GtrR. These results show that the manganese transport protein. MntH modulates a subset of genes and functions regulated by the QS system in B. cenocepacia.

Natural killer cells kill Burkholderia cepacia complex via a contact-dependent and cytolytic mechanism

Burkholderia cepacia complex (Bcc), which includes B. cenocepacia and B. multivorans, pose a life-threatening risk to patients with cystic fibrosis. Eradication of Bcc is difficult due to the high level of intrinsic resistance to antibiotics, and failure of many innate immune cells to control the infection. Because of the pathogenesis of Bcc infections, we wondered if a novel mechanism of microbial host defense involving direct antibacterial activity by natural killer (NK) cells might play a role in the control of Bcc. We demonstrate that NK cells bound Burkholderia, resulting in Src family kinase activation as measured by protein tyrosine phosphorylation, granule release of effector proteins such as perforin and contact-dependent killing of the bacteria. These studies provide a means by which NK cells could play a role in host defense against Bcc infection.

Comparative Genomics of Environmental and Clinical Burkholderia cenocepacia Strains Closely Related to the Highly Transmissible Epidemic ET12 Lineage

The Burkholderia cenocepacia epidemic ET12 lineage belongs to the genomovar IIIA including the reference strain J2315, a highly transmissible epidemic B. cenocepacia lineage. Members of this lineage are able to cause lung infections in immunocompromised and cystic fibrosis patients. In this study, we describe the genome of F01, an environmental B. cenocepacia strain isolated from soil in Burkina Faso that is, to our knowledge, the most closely related strain to this epidemic lineage. A comparative genomic analysis was performed on this new isolate, in association with five clinical and one environmental B. cenocepacia strains whose genomes were previously sequenced. Antibiotic resistances, virulence phenotype, and genomic contents were compared and discussed with an emphasis on virulent and antibiotic determinants. Surprisingly, no significant differences in antibiotic resistance and virulence were found between clinical and environmental strains, while the most important genomic differences were related to the number of prophages identified in their genomes. The ET12 lineage strains showed a noticeable greater number of prophages (partial or full-length), especially compared to the phylogenetically related environmental F01 strain (i.e., 5–6 and 3 prophages, respectively). Data obtained suggest possible involvements of prophages in the clinical success of opportunistic pathogens.

Designing Probes for Immunodiagnostics: Structural Insights into an Epitope Targeting Burkholderia Infections

Structure-based epitope prediction drives the design of diagnostic peptidic probes to reveal specific antibodies elicited in response to infections. We previously identified a highly immunoreactive epitope from the peptidoglycan-associated lipoprotein (Pal) antigen from Burkholderia pseudomallei, which could also diagnose Burkholderia cepacia infections. Here, considering the high phylogenetic conservation within Burkholderia species, we ask whether cross-reactivity can be reciprocally displayed by the synthetic epitope from B. cenocepacia. We perform comparative analyses of the conformational preferences and diagnostic performances of the corresponding epitopes from the two Burkholderia species when presented in the context of the full-length proteins or as isolated peptides. The effects of conformation on the diagnostic potential and cross-reactivity of Pal peptide epitopes are rationalized on the basis of the 1.8 Å crystal structure of B. cenocepacia Pal and through computational analyses. Our results are discussed in the context of designing new diagnostic molecules for the early detection of infectious diseases.

Optimization and characterization of a murine lung infection model for the evaluation of novel therapeutics against Burkholderia cenocepacia

Several B. cenocepacia mouse models are available to study the pulmonary infection by this Burkholderia cepacia complex (BCC) species. However, a characterized B. cenocepacia mouse model to evaluate the efficacy of potential new antibacterial therapies is not yet described. Therefore, we optimized and validated the course of infection (i.e. bacterial proliferation in lung, liver and spleen) and the efficacy of a reference antibiotic, tobramycin (TOB), in a mouse lung infection model. Furthermore, the local immune response and histological changes in lung tissue were studied during infection and treatment. A reproducible lung infection was observed when immunosuppressed BALB/c mice were infected with B. cenocepacia LMG 16656. Approximately 50 to 60% of mice infected with this BCC species demonstrated a dissemination to liver and spleen. TOB treatment resulted in a two log reduction in lung burden, prevented dissemination of B. cenocepacia to liver and spleen and significantly reduced levels of proinflammatory cytokines. As this mouse model is characterized by a reproducible course of infection and efficacy of TOB, it can be used as a tool for the in vivo evaluation of new antibacterial therapies.

Burkholderia cepacia Complex Vaccines: Where Do We Go from here?

Burkholderia comprises a wide variety of environmental Gram-negative bacteria. Burkholderia cepacia complex (Bcc) includes several Burkholderia species that pose a health hazard as they are able to cause respiratory infections in patients with chronic granulomatous disease and cystic fibrosis. Due to the intrinsic resistance to a wide array of antibiotics and naturally occurring immune evasion strategies, treatment of Bcc infections often proves to be unsuccessful. To date, limited work related to vaccine development has been performed for Bcc pathogens. In this review, we have gathered key aspects of Bcc research that have been reported in recent years related to vaccine efforts, virulence, immune responses, and animal models, and use this information to inform the research community of areas of opportunity toward development of a viable Bcc vaccine.

Activator of G-Protein Signaling 3-Induced Lysosomal Biogenesis Limits Macrophage Intracellular Bacterial Infection

Many intracellular pathogens cause disease by subverting macrophage innate immune defense mechanisms. Intracellular pathogens actively avoid delivery to or directly target lysosomes, the major intracellular degradative organelle. In this article, we demonstrate that activator of G-protein signaling 3 (AGS3), an LPS-inducible protein in macrophages, affects both lysosomal biogenesis and activity. AGS3 binds the Gi family of G proteins via its G-protein regulatory (GoLoco) motif, stabilizing the Gα subunit in its GDP-bound conformation. Elevated AGS3 levels in macrophages limited the activity of the mammalian target of rapamycin pathway, a sensor of cellular nutritional status. This triggered the nuclear translocation of transcription factor EB, a known activator of lysosomal gene transcription. In contrast, AGS3-deficient macrophages had increased mammalian target of rapamycin activity, reduced transcription factor EB activity, and a lower lysosomal mass. High levels of AGS3 in macrophages enhanced their resistance to infection by Burkholderia cenocepacia J2315, Mycobacterium tuberculosis, and methicillin-resistant Staphylococcus aureus, whereas AGS3-deficient macrophages were more susceptible. We conclude that LPS priming increases AGS3 levels, which enhances lysosomal function and increases the capacity of macrophages to eliminate intracellular pathogens.

Investigating the Role of the Host Multidrug Resistance Associated Protein Transporter Family in Burkholderia cepacia Complex Pathogenicity Using a Caenorhabditis elegans Infection Model

This study investigated the relationship between host efflux system of the non-vertebrate nematode Caenorhabditis elegans and Burkholderia cepacia complex (Bcc) strain virulence. This is the first comprehensive effort to profile host-transporters within the context of Bcc infection. With this aim, two different toxicity tests were performed: a slow killing assay that monitors mortality of the host by intestinal colonization and a fast killing assay that assesses production of toxins. A Virulence Ranking scheme was defined, that expressed the toxicity of the Bcc panel members, based on the percentage of surviving worms. According to this ranking the 18 Bcc strains were divided in 4 distinct groups. Only the Cystic Fibrosis isolated strains possessed profound nematode killing ability to accumulate in worms’ intestines. For the transporter analysis a complete set of isogenic nematode single Multidrug Resistance associated Protein (MRP) efflux mutants and a number of efflux inhibitors were interrogated in the host toxicity assays. The Bcc pathogenicity profile of the 7 isogenic C. elegans MRP knock-out strains functionality was classified in two distinct groups. Disabling host transporters enhanced nematode mortality more than 50% in 5 out of 7 mutants when compared to wild type. In particular mrp-2 was the most susceptible phenotype with increased mortality for 13 out 18 Bcc strains, whereas mrp-3 and mrp-4 knock-outs had lower mortality rates, suggesting a different role in toxin-substrate recognition. The use of MRP efflux inhibitors in the assays resulted in substantially increased (>40% on average) mortality of wild-type worms.

Intracellular survival ofBurkholderia cepaciacomplex in phagocytic cells

Burkholderia cepacia complex (Bcc) species are a group of Gram-negative opportunistic pathogens that infect the airways of cystic fibrosis patients, and occasionally they infect other immunocompromised patients. Bcc bacteria display high-level multidrug resistance and chronically persist in the infected host while eliciting robust inflammatory responses. Studies using macrophages, neutrophils, and dendritic cells, combined with advances in the genetic manipulation of these bacteria, have increased our understanding of the molecular mechanisms of virulence in these pathogens and the molecular details of cell-host responses triggering inflammation. This article discusses our current view of the intracellular survival of Burkholderia cenocepacia within macrophages.

Efflux pump-mediated drug resistance in Burkholderia

Several members of the genus Burkholderia are prominent pathogens. Infections caused by these bacteria are difficult to treat because of significant antibiotic resistance. Virtually all Burkholderia species are also resistant to polymyxin, prohibiting use of drugs like colistin that are available for treatment of infections caused by most other drug resistant Gram-negative bacteria. Despite clinical significance and antibiotic resistance of Burkholderia species, characterization of efflux pumps lags behind other non-enteric Gram-negative pathogens such as Acinetobacter baumannii and Pseudomonas aeruginosa. Although efflux pumps have been described in several Burkholderia species, they have been best studied in Burkholderia cenocepacia and B. pseudomallei. As in other non-enteric Gram-negatives, efflux pumps of the resistance nodulation cell division (RND) family are the clinically most significant efflux systems in these two species. Several efflux pumps were described in B. cenocepacia, which when expressed confer resistance to clinically significant antibiotics, including aminoglycosides, chloramphenicol, fluoroquinolones, and tetracyclines. Three RND pumps have been characterized in B. pseudomallei, two of which confer either intrinsic or acquired resistance to aminoglycosides, macrolides, chloramphenicol, fluoroquinolones, tetracyclines, trimethoprim, and in some instances trimethoprim+sulfamethoxazole. Several strains of the host-adapted B. mallei, a clone of B. pseudomallei, lack AmrAB-OprA, and are therefore aminoglycoside and macrolide susceptible. B. thailandensis is closely related to B. pseudomallei, but non-pathogenic to humans. Its pump repertoire and ensuing drug resistance profile parallels that of B. pseudomallei. An efflux pump in B. vietnamiensis plays a significant role in acquired aminoglycoside resistance. Summarily, efflux pumps are significant players in Burkholderia drug resistance.

Linking Bacterial Endophytic Communities to Essential Oils: Clues from Lavandula angustifolia Mill

Endophytic bacteria play a crucial role in plant life and are also drawing much attention for their capacity to produce bioactive compounds of relevant biotechnological interest. Here we present the characterisation of the cultivable endophytic bacteria of Lavandula angustifolia Mill.—a species used since antiquity for its therapeutic properties—since the production of bioactive metabolites from medical plants may reside also in the activity of bacterial endophytes through their direct production, PGPR activity on host, and/or elicitation of plant metabolism. Lavender tissues are inhabited by a tissue specific endophytic community dominated by Proteobacteria, highlighting also their difference from the rhizosphere environment where Actinobacteria and Firmicutes are also found. Leaves' endophytic community resulted as the most diverse from the other ecological niches. Overall, the findings reported here suggest: (i) the existence of different entry points for the endophytic community, (ii) its differentiation on the basis of the ecological niche variability, and (iii) a two-step colonization process for roots endophytes. Lastly, many isolates showed a strong inhibition potential against human pathogens and the molecular characterization demonstrated also the presence of not previously described isolates that may constitute a reservoir of bioactive compounds relevant in the field of pathogen control, phytoremediation, and human health.

Identification of new sphingomyelinases D in pathogenic fungi and other pathogenic organisms

Sphingomyelinases D (SMases D) or dermonecrotic toxins are well characterized in Loxosceles spider venoms and have been described in some strains of pathogenic microorganisms, such as Corynebacterium sp. After spider bites, the SMase D molecules cause skin necrosis and occasional severe systemic manifestations, such as acute renal failure. In this paper, we identified new SMase D amino acid sequences from various organisms belonging to 24 distinct genera, of which, 19 are new. These SMases D share a conserved active site and a C-terminal motif. We suggest that the C-terminal tail is responsible for stabilizing the entire internal structure of the SMase D Tim barrel and that it can be considered an SMase D hallmark in combination with the amino acid residues from the active site. Most of these enzyme sequences were discovered from fungi and the SMase D activity was experimentally confirmed in the fungus Aspergillus flavus. Because most of these novel SMases D are from organisms that are endowed with pathogenic properties similar to those evoked by these enzymes alone, they might be associated with their pathogenic mechanisms.

Genomic analysis of three sponge-associated Arthrobacter Antarctic strains, inhibiting the growth of Burkholderia cepacia complex bacteria by synthesizing volatile organic compounds

In this work we analyzed the ability of three Arthrobacter strains (namely TB23, TB26 and CAL618), which were isolated from the Antarctic sponges Haliclonissa verrucosa and Lyssodendrix nobilis, to specifically inhibit the growth of a panel of 40 Burkholderia cepacia complex strains, representing a major cause of infections in patients that are affected by Cystic Fibrosis. The inhibitory activity was due to the synthesis of antimicrobial compounds, very likely volatile organic compounds (VOCs), and was partially dependent on the growth media that were used for Antarctic strains growth. The phylogenetic analysis revealed that two of them (i.e. CAL 618 and TB23) were very close and very likely belonged to the same Arthrobacter species, whereas the strain TB26 was placed in a distant branch. The genome of the strains TB26 and CAL618 was also sequenced and compared with that of the strain TB23. The analysis revealed that TB23 and CAL618 shared more genomic properties (GC content, genome size, number of genes) than with TB26. Since the three strains exhibited very similar inhibition pattern vs Bcc strains, it is quite possible that genes involved in the biosynthesis of antimicrobial compounds very likely belong to the core genome.

A census of RND superfamily proteins in the Burkholderia genus

Aim: The aim of this work was to analyze the eight resistance–nodulation–cell division (RND) families (a group of proteins mainly involved in multidrug resistance of Gram-negative bacteria) in 26 Burkholderia genomes in order to gain knowledge regarding their presence and distribution, to obtain a platform for future experimental tests aimed to identify new molecular targets to be used in antimicrobial therapy against Burkholderia species and to refine the annotation of RND-like sequences in these genomes. Materials & methods: A total of 417 coding sequences were retrieved and analyzed using different bioinformatics tools. Results & conclusion: A complex pattern of RND presence and distribution in the different Burkholderia species was disclosed and a core of proteins represented in all 26 genomes was identified. These ‘core’ proteins might represent useful targets of new synthetic antimicrobial compounds. Furthermore, the annotation of RND-like sequences in Burkholderia was refined.

MtvR is a global small noncoding regulatory RNA in Burkholderia cenocepacia

Burkholderia cenocepacia J2315 is a highly epidemic and transmissible clinical isolate of the Burkholderia cepacia complex (Bcc), a group of bacteria causing life-threatening respiratory infections among cystic fibrosis patients. This work describes the functional analysis of the 136-nucleotide (nt)-long MtvR small noncoding RNA (sRNA) from the Bcc member B. cenocepacia J2315, with homologues restricted to the genus Burkholderia. Bioinformatic target predictions revealed a total of 309 mRNAs to be putative MtvR targets. The mRNA levels corresponding to 17 of 19 selected genes were found to be affected when MtvR was either overexpressed or silenced. Analysis of the interaction between MtvR and the hfq mRNA, one of its targets, showed that the sRNA binds exclusively to the 5' untranslated region (UTR) of the hfq mRNA. This interaction resulted in decreased protein synthesis, suggesting a negative regulatory effect of MtvR on the RNA chaperone Hfq. Bacterial strains with MtvR silenced or overexpressed exhibited pleiotropic phenotypes related to growth and survival after several stresses, swimming and swarming motilities, biofilm formation, resistance to antibiotics, and ability to colonize and kill the nematode Caenorhabditis elegans. Together, the results indicate that the MtvR sRNA is a major posttranscriptional regulator in B. cenocepacia.

Draft genome sequence of the volatile organic compound-producing Antarctic bacterium Arthrobacter sp. strain TB23, able to inhibit cystic fibrosis pathogens belonging to the Burkholderia cepacia complex

Arthrobacter sp. strain TB23 was isolated from the Antarctic sponge Lissodendoryx nobilis. This bacterium is able to produce antimicrobial compounds and volatile organic compounds (VOCs) that inhibit the growth of other Antarctic bacteria and of cystic fibrosis opportunistic pathogens, respectively. Here we report the draft genome sequence of Arthrobacter sp. TB23.