Updated: 3/18/2019

Introduction to Bacterial Virulence

Review Topic
  • Bacterial virulence
    • intrinsic characteristics that influence the bacteria's ability to infect a host
    • methods of increasing virulence
Bacterial Virulence Factors and Examples
Virulence Method
Bacterial Examples

Adhesion and colonization
  • Streptococcus pneumoniae
  • Haemophilus influenzae type b
  • Neisseria spp.
  • IgA protease
  • Cleaves IgA and allows the bacteria to adhere and colonize mucous membranes
  • Escherichia coli
  • Fimbriae
  • Helps adhere and attach to host cells
  • Obligate and facultative intracellular organisms (i.e., Chlamydia spp.)
  • Unknown factors
  • Helps the bacteria invade host cells
Evades immune response by the host
  • Staphylococcus aureus
  • Protein A
  • Prevents phagocytosis by binding to the Fc region of IgG
  • Group A streptococcus
  • Protein M
  • Prevents phagocytosis
  • Streptococcus pneumoniae
  • Capsule
  • Prevents phagocytosis
  • Gram-negative bacteria
  • Endotoxins
  • Exerts many effects, including activation of the complement system, macrophages, and tissue factor
  • Causes sepsis and disseminated intravascular coagulation
  • Some gram-negative and gram-positive bacteria
  • Exotoxins
  • Various effects, depending on the exotoxin, including host cell death, mucosal damage, diarrhea, and neurotoxicity


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