Shigella flexneri

Summary

Shigella Flexneri is a highly virulent bacterium that causes severe intestinal inflammation, leading to bloody diarrhea and dysentery in humans. With over 160 million cases annually, it is especially deadly for children under five. Infection begins through contaminated food or water, where Shigella exploits microfold (M) cells in the intestinal epithelium to gain access to the immune system. The bacteria rapidly reproduce within host cells, spreading from cell to cell, causing widespread damage. Despite its serious impact, no vaccine exists, and antibiotics are ineffective. Improved sanitation is the most effective defense against this deadly pathogen.

Takeaways

• 😀 Shigella Flexneri is a gram-negative bacterium that causes bloody diarrhea and dysentery in humans.
• 😀 Over 160 million cases of Shigellosis occur annually, with more than 1 million deaths, primarily in children under the age of five.
• 😀 Infection is usually caused by ingesting contaminated food, water, or through poor hygiene.
• 😀 Shigella is highly virulent, with as few as 10 bacteria being able to cause disease.
• 😀 The bacteria enter specialized immune cells called M cells in the intestinal epithelium.
• 😀 M cells are located in the follicle-associated epithelium, which is found over Peyer's patches and play a role in immune surveillance.
• 😀 Shigella uses M cells to transport bacteria into the basolateral pocket, where they interact with immune cells.
• 😀 The Type 3 secretion system (T3SS) acts as a molecular needle to inject virulence factors into host cells, triggering host cytoskeletal changes.
• 😀 The bacteria replicate inside vacuoles and use actin comet tails to move within the host cells, spreading the infection from cell to cell.
• 😀 The rapid lateral spread of Shigella infection damages the intestinal epithelium, leading to symptoms like bloody diarrhea.
• 😀 Currently, there is no vaccine for Shigellosis, and antibiotics are ineffective. Improved sanitation is the best defense against the disease.

Q & A

What is Shigella Flexneri and what disease does it cause?

Shigella Flexneri is a gram-negative bacterium that invades the intestinal epithelium, inducing a destructive inflammatory response, leading to bloody diarrhea and a disease known as shigellosis.

How many cases of Shigellosis occur annually, and who is most affected?

There are over 160 million cases of Shigellosis each year, with more than 1 million cases being fatal. The majority of infections (up to 70%) occur in children under the age of five.

What is the primary mode of transmission for Shigella Flexneri?

Shigella Flexneri is primarily transmitted through the ingestion of contaminated food or water or through poor hygiene practices.

How does Shigella Flexneri invade the intestinal cells?

Shigella Flexneri invades the intestinal epithelium by interacting with specialized immune surveillance cells called M cells, which allow the bacterium to pass through the epithelial layer into the underlying immune cells.

What are M cells and what role do they play in Shigella infection?

M cells are specialized cells in the follicle-associated epithelium of the intestine. They sample content from the intestinal lumen and present antigens to immune cells, which Shigella exploits to enter the body and trigger an immune response.

What is the function of the Type 3 secretion system in Shigella Flexneri?

The Type 3 secretion system acts as a molecular needle to inject virulence factors into host cells, triggering cytoskeletal remodeling, which helps the bacterium invade and spread within the host.

What happens after Shigella Flexneri enters a host cell?

Once Shigella enters a host cell, it rapidly reproduces within a vacuole while recruiting host actin to form comet tails. This allows the bacteria to move within the host cell and spread to adjacent cells.

Why is the lateral spread of Shigella infection significant?

The lateral spread of Shigella within the epithelial layer is significant because it allows the bacteria to spread from cell to cell without having to re-enter the basolateral surface, making the infection more widespread and dangerous.

What is the result of Shigella-induced damage to intestinal epithelial cells?

The damage caused by Shigella to intestinal epithelial cells leads to inflammation, edema, and desquamation, resulting in bloody diarrhea.

Why is Shigella infection particularly deadly in children?

Shigella infection is particularly deadly in children, especially in the developing world, because it often coincides with malnutrition, which makes diarrhea more severe and increases the risk of premature death.

What is the current treatment for Shigella infection, and what are its limitations?

Currently, there is no vaccine for Shigella, and antibiotics are often ineffective due to antibiotic resistance. The best defense is improved sanitation.