Shigella flexneri is a facultative bacterium (i.e., it replicates within host ce

Question

Shigella flexneri is a facultative bacterium (i.e., it replicates within host cells, especially in macrophages) that remains an important cause of dysentery (diarrhea) in endemic parts of the world where it is spread through the contamination of the water supply. Although there has been a significant reduction in mortality in young children, morbidity remains unacceptably high. All efforts to develop a vaccine have proven fruitless. Like most pathogenic bacteria, it has acquired a number of virulence factors that enable it to manipulate the immune response to its advantage. Intriguingly, the virulence factors are produced in two stages. The first set of factors enable S. flexneri to infect host Gl epithelium and promote inflammation, which is notable for a robust recruitment of neutrophils. The second stage entails the production of virulence factors that suppress inflammatory responses within host cells, as well as suppressing T-cell activity. EXPLAIN why this two-stage strategy is advantageous to the life cycle of S. flexneri, and why it has been so difficult to generate an effective vaccine.

Explanation / Answer

The two stage strategy is very helpful for S.Flexnneri. Shigella is restricted to Human host only .The shigella is intracellular parasite amd multiply within the colon epithelium cells .the bacteria induce the mucosal cell to phagocyte them and then disrupt phogosome membrane .once they enter in the host cell they colonize the cytoplasm.Icsa a bacterial surface protein activate the host protein .Flexneri develops actin based motility enable pathogen to become efficent at cell to cell spread and cytoplasmic colonization.infected cell mostly attracts neutrophils ,chemokine,and cytokines to damage area which results epithelial layer parmeability ,Now S.Flexneri take advantage for further invasion .

Vaccine :the ability of S.Flexneri to envade epithelial cell and cross talk with immunosystem ,emerging very high resistance .there are so many vaccine trails are going on to amle effective and safe vaccine for the eradication of the bacterium but the poor higene ,multiple stains of bactreium (serotypes)are making the path difficult.

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