Virulence Factors Quiz (BMS Learning Outcomes)

Virulence Factors and Infectious Disease

• Virulence factors are molecules produced by pathogens to cause infections, tissue damage, and evade the immune system.
• These factors include adhesins (attach to host cells), exoenzymes (break down host tissues), and toxins (damage host cells).

Endotoxins vs. Exotoxins

• Endotoxins: Found in the outer membrane of Gram-negative bacteria (Lipid A). They cause general inflammation (fever, shock) and are heat-stable.
• Exotoxins: Protein toxins secreted by bacteria (Gram-positive and some Gram-negative). They target specific cells and tissues, causing damage via precise mechanisms. Exotoxins are heat-labile and highly potent in low doses.

Types of Exotoxins

• Intracellular-targeting toxins (A-B toxins): Enter cells and disrupt specific functions. Examples include diphtheria toxin (inhibits protein synthesis) and botulinum toxin (inhibits neurotransmitter release).
• Membrane-disrupting toxins: Damage host cell membranes by creating pores or degrading phospholipids, causing cell lysis. An example is streptolysin.
• Superantigens: These exotoxins trigger a massive immune response by activating many T cells, leading to a cytokine storm. An example is toxic shock syndrome toxin (TSST).

Viral Adhesion and Antigenic Variation

• Adhesion mechanisms: Viruses use viral proteins (adhesins) to bind to host cell receptors. Examples include Hemagglutinin (Influenza) binding to sialic acid and gp120 (HIV) binding to CD4 and co-receptors.
• Antigenic variation: Viruses evade the immune system by changing surface proteins.
  • Antigenic drift: Small mutations in viral proteins.
  • Antigenic shift: Reassortment of viral genes, creating new strains (influenza).