Endotoxins

Introduction

Bacterial virulence
- intrinsic characteristics that influence the bacterium’s ability to infect a host
- endotoxins are a type of bacterial virulence factor
Endotoxins
- a lipopolysaccharide found in the cell walls of gram-negative organisms
  - heat-stable
- release into the body
  - via cell lysis or detachment from the bacteria
  - not actively secreted (unlike exotoxins)
  - bacterial lysis due to antibiotic treatment can cause a large release of endotoxins
- components
  - O antigen
  - core polysaccharide
  - lipid A
- causes shock, sepsis, DIC, and death
- effects from lipid A component
  - macrophage activation
    - release of IL-1 and IL-6
      - fever
    - release of TNF-alpha
      - fever and hypotension
    - release of nitric oxide
      - hypotension
  - complement activation
    - C3a
      - histamine release, causing hypotension and edema
    - C5a
      - neutrophil chemotaxis
  - tissue factor activation
    - activates coagulation cascade
      - results in disseminated intravascular coagulation

Exotoxins vs Endotoxins
	Exotoxin	Endotoxin
Species that produce the toxin	Some species of gram-positive and gram-negative organisms	Gram-negative organismsListeria
Method of release	Actively secreted	Bacterial cell lysis or fragmentation
Gene location	Plasmid or bacteriophage	Bacterial chromosome
Toxicity level	High toxicity	Low toxicity
Vaccines	Available for some toxins in the form of toxoids	No vaccines available
Properties	Heat-labile	Heat-stable
Examples	Vibrio choleraDiphtheriaSalmonellaShigellaClostridium tetaniClostridium botulinum	Neisseria meningitidisEscherichia coliPseudomonas