What Is Diphtheria? - Cause, Symptoms & Treatments

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  • 0:05 The Mother Ship Bacteria
  • 0:42 Corynebacterium Diphtheriae
  • 1:30 Diphtheriae Toxin
  • 3:11 Signs, Treatment, and…
  • 4:24 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will discuss a bacterium known as Corynebacterium diphtheria, the disease diphtheria, exotoxins, endotoxins, A-B toxins, pseudomembranes, bull-necks, and more!

The Mother Ship Bacteria

As a general rule, invading pathogens, such as bacteria, viruses, fungi and so on, cause a lot of harm on their own. For example, a virus may take over a cell for reproduction, which may end up destroying that cell in the process. Sometimes, however, it's not the pathogen itself that causes a lot of harm, it's what the pathogen releases. I like to think of one particular bacterium as a kind of alien mother ship that shoots out laser beams that end up doing more damage than the mother ship itself.

Corynebacterium Diphtheriae

The mother ship is more formally known as Corynebacterium diphtheriae, which is the gram positive, club-shaped, bacterium responsible for a disease called diphtheria. Diphtheria is an upper respiratory disease characterized by a fever, sore throat and a coating at the back of the nose or throat.

The bacterium responsible for this disease is spread through the respiratory route; meaning, it flies about in the air when someone sneezes and coughs. As soon as another individual inhales this bacterium, they get infected as well. It's quite fitting that this bacterium is spread about in the air, as I said it is like a mother ship, which is something that flies through outer space.

Diphtheriae Toxin

This mother ship shoots out lasers to try and hurt some kind of target. In this case, when the mother ship flies into our upper respiratory tract, like the nose or back of our throat, it will shoot out lasers that end up causing a lot of damage. The lasers that are shot out of this bacterium are more formally called exotoxins. These are toxins that are secreted by bacteria. This is different from an endotoxin, which is a toxin that isn't released by bacteria but is actually part of their cell wall.

The exotoxin released by Corynebacterium diphtheriae is fittingly known as the 'diphtheria toxin'. This toxin, which is a protein, is made of two parts and is known as an 'A-B toxin.' You can liken it to not just any old red laser beam shooting out of the mother ship. Instead, this is a two-colored laser! One part is colored red, the A portion of the A-B toxin, and the other part is colored blue, the B portion of the toxin.

The B portion of the toxin binds to a target cell and allows the A-B toxin entry into the target cell. Once inside, the two parts of the A-B toxin separate. This is where the red part of the laser beam, the A portion of the A-B toxin, begins to exert its damaging effect on the target cell by inhibiting protein synthesis within that cell. If a cell cannot synthesize proteins, it cannot keep itself alive very well.

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