Related Experiment Video
Updated: May 25, 2026
Modeling Tuberculosis in Mycobacterium marinum Infected Adult Zebrafish
Published on: October 8, 2018
ESX-5-deficient Mycobacterium marinum is hypervirulent in adult zebrafish
Eveline M Weerdenburg1, Abdallah M Abdallah, Suman Mitra
1Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, the Netherlands.
Abstract:
ESX-5 is a mycobacterial type VII protein secretion system responsible for transport of numerous PE and PPE proteins. It is involved in the induction of host cell death and modulation of the cytokine response in vitro. In this work, we studied the effects of ESX-5 in embryonic and adult zebrafish using Mycobacterium marinum. We found that ESX-5-deficient M. marinum was slightly attenuated in zebrafish embryos. Surprisingly, the same mutant showed highly increased virulence in adult zebrafish, characterized by increased bacterial loads and early onset of granuloma formation with rapid development of necrotic centres. This early onset of granuloma formation was accompanied by an increased expression of pro-inflammatory cytokines and tissue remodelling genes in zebrafish infected with the ESX-5 mutant. Experiments using RAG-1-deficient zebrafish showed that the increased virulence of the ESX-5 mutant was not dependent on the adaptive immune system. Mixed infection experiments with wild-type and ESX-5 mutant bacteria showed that the latter had a specific advantage in adult zebrafish and outcompeted wild-type bacteria. Together our experiments indicate that ESX-5-mediated protein secretion is used by M. marinum to establish a moderate and persistent infection.
Insights
Mycobacterium tuberculosis ESX-5 secretion system is crucial for persistent infection. Deleting ESX-5 in Mycobacterium marinum attenuated it in embryos but increased virulence in adult zebrafish, outcompeting wild-type strains.
Area of Science:
- Microbiology
- Immunology
- Zebrafish models
Background:
- The ESX-5 secretion system in mycobacteria transports PE and PPE proteins, influencing host cell death and cytokine responses.
- Understanding the role of ESX-5 in vivo is critical for deciphering Mycobacterium marinum pathogenesis.
Purpose of the Study:
- To investigate the in vivo function of the ESX-5 secretion system in zebrafish embryos and adults using Mycobacterium marinum.
- To elucidate the impact of ESX-5 deficiency on bacterial virulence, host immune response, and infection dynamics.
Main Methods:
- Utilized zebrafish (embryonic and adult) and Mycobacterium marinum (wild-type and ESX-5 deficient strains) as model systems.
- Assessed bacterial load, granuloma formation, cytokine expression, and tissue remodeling gene expression.
- Employed RAG-1 deficient zebrafish to evaluate the role of the adaptive immune system.
- Conducted mixed infection experiments to compare the competitive fitness of wild-type and ESX-5 mutant bacteria.
Main Results:
- ESX-5 deficient M. marinum showed slight attenuation in zebrafish embryos.
- The ESX-5 mutant exhibited significantly increased virulence in adult zebrafish, with higher bacterial loads and accelerated granuloma formation.
- Granuloma formation was associated with elevated pro-inflammatory cytokines and tissue remodeling gene expression in ESX-5 mutant infections.
- Increased virulence of the ESX-5 mutant was independent of the adaptive immune system.
- The ESX-5 mutant outcompeted wild-type M. marinum in adult zebrafish, indicating a specific advantage.
Conclusions:
- ESX-5 secretion is essential for Mycobacterium marinum to establish a moderate and persistent infection in adult zebrafish.
- The ESX-5 system plays a complex role in pathogenesis, with distinct functions in different host developmental stages or immune contexts.
- Mycobacterium marinum utilizes ESX-5 to modulate host responses, facilitating long-term colonization rather than acute, destructive infection.
