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How Do the Virulence Factors of Shigella Work Together to Cause Disease?
Emily Mattock1, Ariel J Blocker1
1Faculty of Biomedical Sciences, Schools of Cellular and Molecular Medicine and Biochemistry, University of Bristol Bristol, UK.
Abstract:
Shigella is the major cause of bacillary dysentery world-wide. It is divided into four species, named S. flexneri, S. sonnei, S. dysenteriae, and S. boydii, which are distinct genomically and in their ability to cause disease. Shigellosis, the clinical presentation of Shigella infection, is characterized by watery diarrhea, abdominal cramps, and fever. Shigella's ability to cause disease has been attributed to virulence factors, which are encoded on chromosomal pathogenicity islands and the virulence plasmid. However, information on these virulence factors is not often brought together to create a detailed picture of infection, and how this translates into shigellosis symptoms. Firstly, Shigella secretes virulence factors that induce severe inflammation and mediate enterotoxic effects on the colon, producing the classic watery diarrhea seen early in infection. Secondly, Shigella injects virulence effectors into epithelial cells via its Type III Secretion System to subvert the host cell structure and function. This allows invasion of epithelial cells, establishing a replicative niche, and causes erratic destruction of the colonic epithelium. Thirdly, Shigella produces effectors to down-regulate inflammation and the innate immune response. This promotes infection and limits the adaptive immune response, causing the host to remain partially susceptible to re-infection. Combinations of these virulence factors may contribute to the different symptoms and infection capabilities of the diverse Shigella species, in addition to distinct transmission patterns. Further investigation of the dominant species causing disease, using whole-genome sequencing and genotyping, will allow comparison and identification of crucial virulence factors and may contribute to the production of a pan-Shigella vaccine.
Insights
Shigella bacteria cause bacillary dysentery worldwide. Understanding their virulence factors is key to developing treatments and a potential pan-Shigella vaccine against shigellosis.
Area of Science:
- Microbiology
- Infectious Diseases
- Immunology
Background:
- Shigella is a leading cause of bacillary dysentery globally, with four distinct species causing varied disease severity.
- Shigellosis symptoms include watery diarrhea, abdominal cramps, and fever, driven by bacterial virulence factors.
- Existing knowledge on Shigella virulence factors is fragmented, hindering a comprehensive understanding of disease mechanisms.
Purpose of the Study:
- To synthesize information on Shigella virulence factors and their role in shigellosis.
- To elucidate how these factors contribute to disease symptoms and host immune response.
- To identify crucial virulence factors for potential vaccine development.
Main Methods:
- Review and integration of existing data on Shigella virulence factors.
- Analysis of the mechanisms by which virulence factors induce inflammation, invade host cells, and modulate immune responses.
- Discussion of the potential for whole-genome sequencing and genotyping in future research.
Main Results:
- Shigella employs secreted factors for inflammation and enterotoxicity, causing diarrhea.
- The Type III Secretion System facilitates invasion and destruction of colonic epithelial cells.
- Shigella down-regulates host inflammatory and immune responses to promote infection and re-infection susceptibility.
Conclusions:
- Virulence factor combinations likely explain species-specific disease differences and transmission patterns.
- Further research, including whole-genome sequencing, is needed to identify key virulence factors.
- Identifying these factors could lead to the development of a broad-spectrum Shigella vaccine.