Transcript Bacterial Toxins

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
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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
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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
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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 gramnegative 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.