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Bacterial Toxins

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					Chapter 14 Add-on
 How Bacterial Cells Damage Host Cells
Three mechanisms:
    • Direct Damage
    • Toxins*
    • Hypersensitivity Reactions
* Most bacterial damage is carried out by toxins.
1. Direct Damage
   Some bacteria can induce cells to engulf them (E. coli,
    Shigella, Salmonella, and Neisseria gonorrhoeae).
   Microbial metabolism and multiplication kills host
    cells.
   Other microbes enter the cell by excreting enzymes or
    through their own motility.
2. Toxin Production
   Toxins: Poisonous substances produced by microbes.
   Frequently toxins are the main pathogenic factor.
   Toxigenicity: Ability of a microbe to produce toxins.
   Toxemia: Presence of toxins in the blood.
   Toxin effects: May include fever, cardiovascular
    problems, diarrhea, shock, destruction of red blood
    cells and blood vessels, and nervous system
    disruptions.
   Of 220 known bacterial toxins, 40% damage eucaryotic
    cell membranes.
   Two types of toxins:
    • Exotoxins
    • Endotoxins
A. Exotoxins
• Proteins: Enzymes that carry out specific reactions.
• Soluble in body fluids, rapidly transported throughout
    body in blood or lymph.
•   Produced mainly by gram-positive bacteria.
•   Most genes for toxins are carried on plasmids or
    phages.
•   Produced inside bacteria and released into host tissue.
•   Responsible for disease symptoms and/or death.
    Cytotoxins: Kill or damage host cells.
    Neurotoxins: Interfere with nerve impulses.
    Enterotoxins: Affect lining of gastrointestinal tract.
•   Antibodies called antitoxins provide immunity.
•   Toxoids: Toxins that have been altered by heat or
    chemicals. Used as vaccines for diphtheria and
    tetanus.
  Important Exotoxins
Diphtheria Toxin: Corynebacterium diphtheriae when infected
 by a phage carrying tox gene. Cytotoxin inhibits protein
 synthesis in eucaryotic cells. Two polypeptides: A (active) and
 B (binding).
Erythrogenic Toxins: Streptococcus pyogenes produces three
 cytotoxins which damage blood capillaries, causing a red rash.
Botulinum Toxins: Produced by Clostridium botulinum.
 Neurotoxin that inhibits release of neurotransmitter
 acetylcholine and prevents transmission of nerve impulses to
 muscles, causing flaccid paralysis. Extremely potent toxins.
Tetanus Toxin: Produced by Clostridium tetani. A neurotoxin
 that blocks relaxation of skeletal muscles, causing
 uncontrollable muscle spasms (lockjaw) and convulsions.
Vibrio Enterotoxin: Produced by Vibrio cholerae. Two
 polypeptides: A (active) and B (binding). The A subunit of
 enterotoxin causes epithelial cells to discharge large amounts
 of fluids and electrolytes.
Staphylococcal Enterotoxin: Staphylococcus aureus produces an
 enterotoxin similar to cholera toxin. Other enterotoxins cause
 toxic shock syndrome.
Muscle Spasms of Tetanus are Caused
 by Neurotoxin of Clostridium tetani




Neonatal Tetanus (Wrinkled brow and risus sardonicus)
Source: Color Guide to Infectious Diseases, 1992
Vibrio Enterotoxin Causes Profuse Watery Diarrhea




Rice-water stool of cholera. The A subunit of enterotoxin causes
epithelial cells to discharge large amounts of fluids and electrolytes.
Source: Tropical Medicine and Parasitology, 1995
Scalded Skin Syndrome   Toxic Shock Syndrome
                  Endotoxins
• Part    of outer membrane surrounding gram-
  negative bacteria.
• Endotoxin is lipid portion of lipopolysaccharides
  (LPS), called lipid A.
• Effect exerted when gram-negative cells die and
  cell walls undergo lysis, liberating endotoxin.
• All produce the same signs and symptoms:
   Chills, fever, weakness, general aches, blood
    clotting and tissue death, shock, and even death.
    Can also induce miscarriage.
   Fever:     Pyrogenic response is caused by
    endotoxins.
         Endotoxins (Continued)
• Endotoxins do not promote the formation of
  effective antibodies.
• Organisms that produce endotoxins include:
  Salmonella typhi
  Proteus spp.
  Pseudomonas spp.
  Neisseria spp.
• Medical equipment that has been sterilized
 may still contain endotoxins.
  Limulus amoebocyte assay (LAL) is a test used to
   detect tiny amounts of endotoxin.

				
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