umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Drosophila melanogaster as a model for elucidating the pathogenicity of Francisella tularensis
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Clinical Bacteriology.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Clinical Bacteriology.
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics. Umeå University, Faculty of Social Sciences, Department of Statistics. Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Clinical Bacteriology. (Computational Life Science Cluster (CLiC))
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Clinical Bacteriology.
Show others and affiliations
2008 (English)In: Cellular Microbiology, ISSN 1462-5814, E-ISSN 1462-5822, Vol. 10, no 6, 1327-1338 p.Article in journal (Refereed) Published
Abstract [en]

Drosophila melanogaster is a widely used model organism for research on innate immunity and serves as an experimental model for infectious diseases. The aetiological agent of the zoonotic disease tularaemia, Francisella tularensis, can be transmitted by ticks and mosquitoes and Drosophila might be a useful, genetically amenable model host to elucidate the interactions between the bacterium and its arthropod vectors. We found that the live vaccine strain of F. tularensis was phagocytosed by Drosophila and multiplied in fly haemocytes in vitro and in vivo. Bacteria injected into flies resided both inside haemocytes and extracellularly in the open circulatory system. A continuous activation of the humoral immune response, i.e. production of antimicrobial peptides under control of the imd/Relish signalling pathway, was observed and it may have contributed to the relative resistance to F. tularensis as flies defective in the imd/Relish pathway died rapidly. Importantly, bacterial strains deficient for genes of the F. tularensis intracellular growth locus or the macrophage growth locus were attenuated in D. melanogaster. Our results demonstrate that D. melanogaster is a suitable model for the analysis of interactions between F. tularensis and its arthropod hosts and that it can also be used to identify F. tularensis virulence factors relevant for mammalian hosts.

Place, publisher, year, edition, pages
2008. Vol. 10, no 6, 1327-1338 p.
National Category
Microbiology in the medical area
Research subject
Clinical Bacteriology
Identifiers
URN: urn:nbn:se:umu:diva-9517DOI: 10.1111/j.1462-5822.2008.01129.xPubMedID: 18248629 [PubMed - as supplied by publisher]OAI: oai:DiVA.org:umu-9517DiVA: diva2:149188
Available from: 2008-04-14 Created: 2008-04-14 Last updated: 2017-12-14
In thesis
1. Host-pathogen interactions between Francisella tularensis and Drosophila melanogaster
Open this publication in new window or tab >>Host-pathogen interactions between Francisella tularensis and Drosophila melanogaster
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Francisella tularensis is a highly virulent Gram-negative bacterium causing the zoonotic disease tularemia. Arthropod-borne transmission plays an important role in transferring the disease to humans. F. tularensis induces very low amounts of pro-inflammatory cytokines during infection, due to inhibition of immune signaling pathways and an unusual structure of its lipopolysaccharide (LPS). To date, there is no vaccine available that is approved for public use, although an attenuated live vaccine strain (LVS) is commonly used as a model of the more infectious Francisella strains. To produce an effective vaccine it is important to understand the lifecycle of F. tularensis, including the interaction with the arthropod hosts. Drosophila melanogaster is a widely used model organism, which is increasingly being used in host-pathogen interaction studies as the immune pathways in flies are evolutionary conserved to the immune pathways in humans. An important part of the immune defense of D. melanogaster as well as of arthropods in general is the production of antimicrobial peptides. These peptides primarily target the bacterial membrane, inhibiting bacterial proliferation or directly killing the bacteria.

The aim of this thesis was to establish D. melanogaster as a model for F. tularensis infection and as a model for arthropod vectors of F. tularensis. Also, to use D. melanogaster to further study the interaction between F. tularensis and arthropod vectors, with specific regard to the host immune signaling and arthropod antimicrobial peptides.

F. tularensis LVS infects and kills D. melanogaster in a dose-dependent manner. During an infection, bacteria are found inside fly hemocytes, phagocytic blood cells, similar as in human infections. In mammals genes of the intracellular growth locus (igl) are important for virulence. In this work it is shown that the igl genes are also important for virulence in flies. These results demonstrate that D. melanogaster can be used as a model to study F. tularensis-host interactions.

LVS induces a prolonged activation of several immune signaling pathways in the fly, but seem to interfere with the JNK signaling pathway, similarly as in mammals. Overexpression of the JNK pathway in flies has a protective effect on fly survival.

Relish mutant flies, essentially lacking a production of antimicrobial peptides, succumb quickly to a F. tularensis infection, however, F. tularensis is relatively resistant to individual D. melanogaster antimicrobial peptides. Overexpressing antimicrobial peptide genes in wildtype flies has a protective effect on F. tularensis infection, suggesting that a combination of several antimicrobial peptides is necessary to control F. tularensis. The production of numerous antimicrobial peptides might be why D. melanogaster survives relatively long after infection. An intact structure of the lipid A and of the Kdo core of Francisella LPS is necessary for resistance to antimicrobial peptides and full virulence in flies. These results are similar to previous studies in mammals. In contrast to studies in mammals, genes affecting the O-antigen of F. tularensis LPS are not necessary for virulence in flies.

In conclusion, this thesis work shows that D. melanogaster can be used as a model for studying F. tularensis-host interactions. LVS activates several immune pathways during infection, but interfere with the JNK pathway. Overexpressing the JNK pathway results in increased survival of flies infected with LVS. Despite rather high resistance to individual antimicrobial peptides, exposure to a combination of several D. melanogaster antimicrobial peptides reduces the virulence of F. tularensis.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2012. 45 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1504
Keyword
arthropod vector, JNK, lipopolysaccharide, antimicrobial peptides
National Category
Microbiology in the medical area
Research subject
Clinical Bacteriology; Molecular Biology
Identifiers
urn:nbn:se:umu:diva-54604 (URN)978-91-7459-432-4 (ISBN)
Public defence
2012-05-25, E04, by 6E, Norrlands universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2012-05-04 Created: 2012-05-02 Last updated: 2012-05-04Bibliographically approved
2. Effects of Francisella tularensis infection on macrophage intracellular signaling
Open this publication in new window or tab >>Effects of Francisella tularensis infection on macrophage intracellular signaling
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microbes contain a number of structural components, also known as pathogen associated molecular patterns (PAMP), which can be recognized by the host defense system. The PAMP serve as ligands for Toll-like receptors (TLR) expressed on phagocytic cells. Binding of PAMP to TLR leads to activation of a number of intracellular transduction pathways including NF-�B and mitogen-activated protein kinase pathways (MAPK). Activation of those pathways in turn leads to activation of proinflammatory immune responses and antimicrobial defense mechanisms. In this study we show that the intracellular pathogen F. tularensis LVS can induce a proinflammatory response during internalization in both human and mouse macrophages. However, after internalization, F. tularensis LVS effectively blocks all these pathways resulting in no secretion of proinflammatory cytokines in mouse macrophages. In human macrophages, a downregulation was observed, however, there was not a complete block as in the murine cells. Furthermore, the infected cells do not become activated by stimulation with TLR agonists such as Escherichia coli LPS or bacterial lipoprotein. This phenomenon is observed only when the cells were infected with the LVS strain, but not with killed bacteria or specific mutants such as iglC, or mglA mutants, suggesting that not only their presence but also rapid regulation of the Igl proteins are needed. Thus, Igl/Mgl system plays a very important role in mediating these inhibitory effects. To further investigate the role of the Igl/Mgl proteins in the virulence of F. tularensis, we established a novel model for tularemia, infection of Drosophila melanogaster. Using the fly model as a way to mimic the F. tularensis infection in arthropod vectors, which are important for its life cycle, we observed that bacterial mutants in each of the IglB, IglC, IglD, or MglA proteins all showed less efficient killing of the flies than did the parental LVS strain. Nitric oxide, superoxide, and the reaction product of the two mediators, peroxynitrite, all are important for regulation of eukaryotic cell signaling and effectuating bactericidal mechanisms. To this end, we investigated the role of these mediators for the F. tularensismediated TLR-signaling inhibition. We observed that whereas peroxynitrite had little effect on the inhibition, addition of SNAP, a donor of nitric oxide, partially restored the ability of the cells to respond to LPS stimulation and secrete proinflammatory cytokine such as TNF-�. However, since FeTTPS reversed the SNAP-mediated effect, the results indicate that NO forms peroxynitrite intracellular and that the latter molecule is the effector. Together these results indicate that F. tularensis contains PAMP that can activate proinflammatory immune response while the bacteria are located outside of phagocytic cell and during internalization, however, the intracellular bacteria have means to inhibit the activation of anti-bacterial systems of macrophages and block inflammatory responses completely in mouse cells and partially in human cells. This suppression may lead to disruption of synthesis of bactericidal effector molecules, allowing F. tularensis to survive and rapidly proliferate inside phagocytic cells. The ability to suppress the inflammatory responses is dependent on expression of the Igl/Mgl proteins. The Igl/Mgl system is also critical for the ability of F. tularensis to replicate in mammalian cells and in D. melanogaster.

Place, publisher, year, edition, pages
Umeå: Klinisk mikrobiologi, 2005. 55 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 960
Research subject
Clinical Bacteriology
Identifiers
urn:nbn:se:umu:diva-547 (URN)91-7305-898-3 (ISBN)
Public defence
2005-05-31, Sal E04, NUS, By 6E, Umeå, 09:00 (English)
Opponent
Available from: 2005-05-31 Created: 2005-05-31 Last updated: 2012-06-28Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textPubMedhttp://www.ncbi.nlm.nih.gov/pubmed/18248629?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

Search in DiVA

By author/editor
Vonkavaara, MalinTelepnev, Maxim VRydén, PatrikSjöstedt, AndersStöven, Svenja
By organisation
Clinical BacteriologyDepartment of Mathematics and Mathematical StatisticsDepartment of Statistics
In the same journal
Cellular Microbiology
Microbiology in the medical area

Search outside of DiVA

GoogleGoogle Scholar

doi
pubmed
urn-nbn

Altmetric score

doi
pubmed
urn-nbn
Total: 155 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf