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Evidence that host-recycling of Mycobacterium avium preserves its ability to hinder macrophage killing functions
C Fréhel1, M F Thorel, N Rastogi
1Unité de Microscopie Electronique, Institut Pasteur, Paris.
Abstract:
The opportunistic pathogen Mycobacterium avium was selected as a model for the study of the bacterial cell envelope and resistance to macrophage killing functions. We hereby demonstrate that characteristic features of M. avium, e.g. existence of a polysaccharide-rich outer layer (POL), presence of a protective capsule also called electron-transparent zone (ETZ) around phagocytized bacteria, and inhibition of phagosome-lysosome fusions (PLF), were better expressed by bacteria recently isolated from infected rabbits than by bacteria subcultured in laboratory media. Our data appeared to confirm previous suggestions that M. avium regulatory mechanisms are such that during laboratory growth of these bacteria, synthesis of surface components which may be important concerning their virulence properties, is effectively diminished.
Insights
Mycobacterium avium virulence factors, including its polysaccharide-rich outer layer (POL) and protective capsule (ETZ), are diminished in lab-grown cultures. Recently isolated M. avium from rabbits better expressed these traits and inhibited phagosome-lysosome fusion (PLF).
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Mycobacterium avium is an opportunistic pathogen.
- Understanding its cell envelope and macrophage resistance is crucial.
- Virulence factors may be affected by laboratory cultivation.
Purpose of the Study:
- To investigate the expression of M. avium virulence factors.
- To compare recently isolated bacteria with laboratory-cultured strains.
- To understand M. avium's resistance to macrophage killing functions.
Main Methods:
- Comparative analysis of M. avium strains.
- Characterization of bacterial cell envelope components.
- Assessment of phagosome-lysosome fusion inhibition.
Main Results:
- Bacteria recently isolated from infected rabbits exhibited enhanced expression of a polysaccharide-rich outer layer (POL) and a protective capsule (ETZ).
- These recently isolated strains also demonstrated a greater inhibition of phagosome-lysosome fusion (PLF).
- Laboratory-subcultured M. avium showed diminished synthesis of surface components important for virulence.
Conclusions:
- Laboratory cultivation significantly reduces the expression of key M. avium virulence factors.
- M. avium regulatory mechanisms downregulate the synthesis of surface components during in vitro growth.
- This highlights the importance of using recently isolated strains for studying M. avium virulence and host-pathogen interactions.
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