Gram Negative Bacteria: Shigella

Summary

In this video, we explore the characteristics, pathogenesis, and clinical significance of Shigella, a gram-negative bacterium. Key features include its non-motility, inability to ferment lactose, and the absence of flagella. Shigella's virulence factors include endotoxins and the production of Shiga toxin, which damages cells by inhibiting protein synthesis. The infection, known as shigellosis, causes acute bloody diarrhea and can lead to hemolytic-uremic syndrome (HUS), especially with Shigella dysenteriae. HUS results in kidney failure, anemia, and low platelet count, affecting mainly children under 10. Stay tuned for more in-depth microbiology content!

Takeaways

• 😀 Shigella is a gram-negative, non-motile, non-lactose fermenter that is negative for oxidase and does not produce hydrogen sulfide on TSI agar.
• 😀 Shigella grows as colorless colonies on MacConkey’s agar and green colonies on Hektoen’s agar due to its non-lactose fermenting nature.
• 😀 Shigella has endotoxins, as it is a gram-negative bacterium, but lacks flagella, making it non-motile.
• 😀 Despite lacking flagella, Shigella can invade and move within the intestinal epithelium using a unique mechanism where it propels itself through cells.
• 😀 Shiga toxin, produced by some species of Shigella, binds to the 60S ribosomal subunit to inhibit protein synthesis, causing cell damage.
• 😀 Shigellosis is characterized by acute bloody diarrhea caused by Shigella's invasion and damage to intestinal cells.
• 😀 Shigella enters the intestinal cells by first being taken up by M cells and then using actin filaments to move laterally to adjacent cells.
• 😀 Shigella infection causes inflammatory diarrhea with blood and neutrophils in the stool due to immune system activation and cell damage.
• 😀 Shigella dysenteriae can cause hemolytic-uremic syndrome (HUS), which involves hemolytic anemia, acute kidney failure, and low platelet count.
• 😀 HUS results from Shiga toxin-induced damage to endothelial cells, leading to kidney failure, platelet aggregation, and destruction of red blood cells.
• 😀 Children under 10 years old are particularly at risk for developing HUS following a Shigella dysenteriae infection.

Q & A

What is Shigella, and how is it classified in terms of its bacterial characteristics?

Shigella is a gram-negative, non-motile, non-lactose fermenting rod-shaped bacterium. It is oxidase-negative and does not produce hydrogen sulfide on TSI (Triple Sugar Iron) agar.

Why is Shigella referred to as being 'negative to everything'?

Shigella is often described as 'negative to everything' because it lacks several key characteristics, such as motility, lactose fermentation, oxidase activity, and hydrogen sulfide production, which distinguishes it from other bacteria.

What does Shigella look like on MacConkey’s agar and Hektoen’s agar?

On MacConkey’s agar, Shigella forms colorless colonies, as it is a non-lactose fermenter. On Hektoen’s agar, it produces green colonies.

What are the virulence factors of Shigella?

Shigella has endotoxins, as it is a gram-negative bacterium. However, it lacks the H antigen (flagella), meaning it cannot move. Despite this, it has a unique mechanism for invading and moving within intestinal cells.

How does Shigella move and invade intestinal cells despite being non-motile?

Shigella invades intestinal cells by inducing the uptake of the bacteria by M cells, and once inside the cells, it propels itself from one cell to another by manipulating actin filaments, which allows it to move like a rocket.

What is Shiga toxin, and what does it do to the cells?

Shiga toxin, produced by some species of Shigella, binds to the 60S ribosomal subunit in cells, inhibiting protein synthesis and causing cellular damage.

What is shigellosis, and what are its main symptoms?

Shigellosis is the infection caused by Shigella, characterized by acute bloody diarrhea. It results from inflammation in the intestines, triggered by Shigella's invasion and cytotoxic effects.

How does Shigella cause the bloody diarrhea observed in shigellosis?

Shigella damages the intestinal epithelial cells, leading to the release of inflammatory cytokines and the recruitment of neutrophils, causing inflammation. This results in bloody diarrhea with the presence of neutrophils in the stool.

What is Hemolytic-Uremic Syndrome (HUS), and how is it linked to Shigella dysenteriae?

Hemolytic-Uremic Syndrome (HUS) is a condition characterized by hemolytic anemia, acute kidney failure (uremia), and low platelet counts. It can be caused by Shigella dysenteriae, which produces Shiga toxin that damages endothelial cells, including those in the kidneys, leading to HUS.

Which other bacteria produce toxins similar to Shiga toxin and also cause HUS?

Enterohemorrhagic Escherichia coli (EHEC) is another gram-negative bacterium that produces a toxin similar to Shiga toxin and can cause Hemolytic-Uremic Syndrome (HUS).