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Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection
Published on: November 22, 2013
Legionella pneumophila pathogenesis in the Galleria mellonella infection model
Clare R Harding1, Gunnar N Schroeder, Stuart Reynolds
1Centre for Molecular Microbiology and Infection, Division of Cell and Molecular Biology, Imperial College London, London, United Kingdom.
Abstract:
Legionella pneumophila is a facultative intracellular human pathogen and the etiological agent of severe pneumonia known as Legionnaires' disease. Its virulence depends on protein secretion systems, in particular, the Dot/Icm type IV secretion system (T4SS), which is essential to establish a replication-permissive vacuole in macrophages. The analysis of the role of these systems and their substrates for pathogenesis requires easy-to-use models which approximate human infection. We examined the effectiveness of the larvae of the wax moth Galleria mellonella as a new model for L. pneumophila infection. We found that the L. pneumophila strains 130b, Paris, and JR32 caused mortality of the G. mellonella larvae that was strain, infectious dose, growth phase, and T4SS dependent. Wild-type L. pneumophila persisted and replicated within the larvae, whereas T4SS mutants were rapidly cleared. L. pneumophila strain Lp02, which is attenuated in the absence of thymidine but has a functional T4SS, resisted clearance in G. mellonella up to 18 h postinfection without inducing mortality. Immunofluorescence and transmission electron microscopy revealed that L. pneumophila resided within insect hemocytes in a vacuole that ultrastructurally resembled the Legionella-containing vacuole (LCV) observed in macrophages. The vacuole was decorated with the T4SS effector and LCV marker SidC. Infection caused severe damage to the insect organs and triggered immune responses, including activation of the phenoloxidase cascade leading to melanization, nodule formation, and upregulation of antimicrobial peptides. Taken together, these results suggest that G. mellonella provides an effective model to investigate the interaction between L. pneumophila and the host.
Insights
The wax moth Galleria mellonella serves as a novel model for studying Legionella pneumophila infections, demonstrating bacterial persistence and host immune responses relevant to human disease.
Area of Science:
- Microbiology
- Pathogenesis
- Infectious Disease Immunology
Background:
- Legionella pneumophila causes Legionnaires' disease, a severe pneumonia.
- The Dot/Icm type IV secretion system (T4SS) is crucial for L. pneumophila virulence.
- Developing accessible models for L. pneumophila pathogenesis is essential.
Purpose of the Study:
- To evaluate the wax moth Galleria mellonella larvae as a model for L. pneumophila infection.
- To investigate the role of the T4SS in L. pneumophila pathogenesis within this model.
- To characterize L. pneumophila-host interactions in G. mellonella.
Main Methods:
- Infection of G. mellonella larvae with different L. pneumophila strains.
- Assessment of larval mortality, bacterial persistence, and replication.
- Microscopic analysis (immunofluorescence, TEM) of intracellular bacteria and host responses.
- Analysis of host immune reactions (melanization, antimicrobial peptides).
Main Results:
- L. pneumophila strains caused T4SS-dependent mortality in G. mellonella.
- Wild-type bacteria persisted and replicated, while T4SS mutants were cleared.
- Bacteria resided in vacuoles resembling Legionella-containing vacuoles (LCVs) in hemocytes.
- Infection induced insect organ damage and immune responses like melanization.
Conclusions:
- Galleria mellonella larvae provide a viable and informative model for L. pneumophila pathogenesis studies.
- The T4SS is critical for L. pneumophila survival and virulence in this insect model.
- This model facilitates investigation into host-pathogen interactions and immune responses.
