Weapons of War

Lecture Overview: Weapons of War - Toxins, Secretion Systems and Virulence Factors

What is a Virulence Factor?

  • Components that enable bacteria to establish infections and cause disease.

Bacterial Toxins (Key Examples)

  1. Cholera Toxin - causes severe dehydrating diarrhea.

  2. Pneumolysin - primarily affects respiratory systems, causing cell lysis.

  3. Shiga Toxin - inhibits protein synthesis; linked to bloody diarrhea and hemolytic uremic syndrome.

  4. Botulinum Toxin - causes flaccid paralysis by blocking acetylcholine release.

Stages of Infection

  1. Transmission - sharing pathogenic bacterium.

  2. Adhesion - binding to host cells (e.g., P fimbriae).

  3. Entry - pathogens invade host.

  4. Invasion - deeper penetration into tissues.

  5. Immune Evasion - avoiding host immune responses (e.g., capsules).

  6. Host Damage - causing disease symptoms.

  7. Competition - outcompeting host microbes for resources.

Role of Toxins in Virulence

  • Toxins serve varied roles including immune evasion, direct damage to host cells, and facilitating transmission.

Key Secretion Systems in Bacteria

  • Type III Secretion System (T3SS): A needle-like structure that injects proteins directly into host cells, manipulating their functions.

  • Type VI Secretion System (T6SS): Fires toxins at competing bacteria or host cells, aiding in bacterial competition and colonization.

Summary of Key Toxins

Toxin

Produced By

Structure

Action

Effect on Host

Role in Disease/ Transmission

Cholera toxin

Vibrio cholerae

AB5 Toxin

Increases cAMP

Watery diarrhea

Transmission via stool

Shiga toxin

Shigella dysenteriae / E. coli O157:H7

AB5 Toxin

Inhibits protein synthesis

Cell death, bloody diarrhea

Local gut damage, renal complications

Botulinum toxin

Clostridium botulinum

Two-chain toxin

Cleaves SNARE proteins

Flaccid paralysis

Creates environment for spores

Pneumolysin

Streptococcus pneumoniae

Pore-forming toxin

Cell lysis

Inflammation and immune modulation

Aids colonization and transmission

Applications of Toxins in Medicine

  • Medical Therapeutics: Botox for dystonia; engineered toxins for cancer therapy.

  • Vaccines: Use of toxoids for immunization strategies.