Toxins and Toxin Mediated Disease
Growth in broth:
Pellet (bacterial cells)
Supernatant (Cell free)
Administer to animal or human. If toxic then:
Endotoxin = Lipopolysaccharide (LPS)
Exotoxins - Classification:
- Membrane damaging
- Protein synthesis inhibitors
By organ target:
- Enterotoxin, Cardiac, Hepatic or Renal toxic effects
- Lipases (a)
- Pore-forming (a)
- Cholera, E. coli LT (c, E)
- Diphtheria toxin (b, C,N)
- Psuedomonas Exotoxin A (b)
- Pertussis toxin (c)
- Zinc Proteases
- Tetanus, botulinum
- Glycosyl transferases
- Clostridium difficile
- Others+++ e.g. Adenyl cyclase, superantigenic toxins
Common features of exotoxins:
Active and Binding portions (may be on separate subunits).
Hence same enzyme activity with different Binding specificity produces a different
pattern of toxicity.
Similarly, toxins with essentially the same enzyme activity may have active
units that have different substrate specificities.
The active subunits often require proteolysis before they
- Pathology often distant from site of bacterial growth.
- Protective immunity may be mediated by anti-toxin antibodies alone.
- Disease may be fully reproduced by administering the toxin alone.
Toxin mediated diseases come in 3 forms:
- Disease due to preformed toxin (toxin formed outside the body)
e.g. S. aureus food poisoning, botulism (Clostridium botulinum).
- Disease due (almost) entirely to toxin formation during infection
e.g. tiphtheria (Corynebacterium diphtheriae), tetanus (Clostridium
- Disease to which toxin(s) make a significant contribution but other virulence
factors are very important
e.g. cholera (Vibrio cholerae), whooping cough (Bordetella pertussis).
- Gram negative septic (endotoxic) shock, a toxin-cytokine mediated
disease caused by any gram negative organism in the bloodstream in high numbers.
- Toxic shock syndrome, a toxin-cytokine mediated disease (Staphylococcus
aureus, Streptococcus pyogenes) - only strains producing superantigenic
Example 7: Diphtheria
- Corynebacterium diphtheriae, Gram positive bacillus causing severe
pharyngitis plus heart and nerve pathology.
- Subunit ADP ribosylating toxin which inhibits protein synthesis and damages
the respiratory system, heart and nervous system.
Example 9: Cholera
- Vibrio cholerae, Gram negative curved bacillus.
- Subunit ADP-ribosylating toxin leading to massive chloride and water secretion
in the small intestine.
© MicrobiologyBytes 2007.