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.