I. BACTERIAL PATHOGENESIS

C. VIRULENCE FACTORS THAT DAMAGE THE HOST

2. Producing Harmful Exotoxins: An Overview

Fundamental Statements for this Learning Object:

1. Exotoxins are toxins, often protein in nature, secreted from a living bacterium.
2. Some bacteria use various secretion systems to inject toxins directly into human cells.
3. There are three main types of exotoxins: superantigens (type I toxins); exotoxins that damage host cell membranes (type II toxins); and A-B toxins and other toxin that interfere with host cell function (type III toxins).
4. The body's major defense against exotoxins is the production of antitoxin antibodies. Once the antibody binds to the exotoxin, the toxin can no longer bind to the receptors on the host cell membrane.

 

LEARNING OBJECTIVES FOR THIS SECTION

In this section on Bacterial Pathogenesis we are looking at virulence factors that damage the host. Virulence factors that damage the host include:

1. The ability to produce Pathogen-Associated Molecular Patterns or PAMPs that bind to host cells causing them to synthesize and secrete inflammatory cytokines and chemokines;

2. The ability to produce harmful exotoxins.

3. The ability to induce autoimmune responses.

We will now look at the ability of bacteria to produce harmful exotoxins.

The Ability to Produce Harmful Exotoxins: An Overview

Exotoxins (def) are toxins, often proteins in nature, secreted from a living bacterium but also released upon bacterial lysis. In addition, some bacteria use various secretion systems such as the type 3 secretion system to inject toxins directly into human cells. (As learned earlier, the lipopolysaccharide or LPS portion of the Gram-negative bacterial cell wall is known as endotoxin (def), a PAMP that can initiate an excessive inflammatory response in the host. It was originally called endotoxin because it was located within the Gram-negative cell wall as opposed to being secreted from bacteria as in the case of exotoxins.)

Not all exotoxins are necessarily produced to harm humans. Some may be designed to play a role in bacterial physiology, such as resisting bacteriophages, regulating cellular function, or quorum sensing. Other toxins may be produced primarily to target protozoa, insects, and smaller animals and harming human cells becomes an accidental side effect.

There are three main types of exotoxins:

1. superantigens (Type I toxins);

2. exotoxins that damage host cell membranes (Type II toxins); and

3. A-B toxins and other toxin that interfere with host cell function (Type III toxins).

 

The body's major defense against exotoxins is the production of antitoxin antibodies. Once the antibody binds to the exotoxin, the toxin can no longer bind to the receptors on the host cell membrane.

html5 animation showing the neutralization of exotoxins with antibodies. by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 Please send comments and inquiries to Dr. Gary Kaiser

We will now look at each of these three types of exotoxins.

 

• QUIZ YOURSELF ON THIS SECTION

Gary E. Kaiser, Ph.D.
Professor of Microbiology
The Community College of Baltimore County, Catonsville Campus
This work is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html.