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Understanding Bacterial Virulence Factors

Apr 23, 2025

Introduction to Bacterial Virulence

Overview

  • Bacterial virulence refers to intrinsic characteristics influencing a bacteria's ability to infect a host.
  • Involves methods to increase virulence through specific factors and mechanisms.

Bacterial Virulence Factors and Examples

Adhesion and Colonization

  • Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria spp.
    • Factor: IgA protease
    • Function: Cleaves IgA, facilitating adherence and colonization of mucous membranes.
  • Escherichia coli
    • Factor: Fimbriae
    • Function: Aids in adherence and attachment to host cells.

Invasion

  • Obligate and facultative intracellular organisms (e.g., Chlamydia spp.)
    • Factors: Unknown
    • Function: Assists bacteria in invading host cells.

Evasion of Host Immune Response

  • Staphylococcus aureus
    • Factor: Protein A
    • Function: Binds to the Fc region of IgG, preventing phagocytosis.
  • Group A Streptococcus
    • Factor: Protein M
    • Function: Inhibits phagocytosis.
  • Streptococcus pneumoniae
    • Factor: Capsule
    • Function: Inhibits phagocytosis.

Toxins

  • Gram-negative bacteria
    • Toxin Type: Endotoxins
    • Effects: Activates complement system, macrophages, tissue factor, leading to sepsis and disseminated intravascular coagulation.
  • Gram-negative and Gram-positive bacteria
    • Toxin Type: Exotoxins
    • Effects: Varies by exotoxin; can cause host cell death, mucosal damage, diarrhea, and neurotoxicity.