2.2.4. Neurotoxins

Question 1

Anaerobic, Gram Positive, spore-forming rods are characteristic features of which bacterial genus?

Answer 1

Clostridia

Question 2

What does it mean for Clostridia (or any other microbe) to be an “anaerobe”?

Answer 2

It can’t use O2 as a final electron acceptor

Question 3

What enzyme do strict anaerobes (like Clostridia) LACK? What does this enzyme do?

Answer 3

Superoxide dismutase - this enzyme neutralizes toxic superoxide anions that accumulate in the presence of O2

Question 4

List SIX medically-relevant agents related to Clostridia.

Hint: this includes toxin(s) and disease(s)

Answer 4

1- Botulism

2- Tetanus

3- Gas gangrene

4- Food poisoning

5- Clostridium difficile-associated disease (CDAD)

6- Pseudomembranous colitis

Question 5

Describe TWO general features of bacterial spores that make them “hardy”, or resistant to destruction

Answer 5

1- Spores are DENSE

2- Spores have MANY OUTER LAYERS

NOTE: Just the package that makes the rod via germination. The rod makes the toxins, not the spore.

Question 6

List the three types of spores that Clostridia can form.

Hint: these are based on the spore’s location

Answer 6

1- Tetanus (think of tennis rackets)

2- Gas Gangrene Tetanus

3- Botulinum

Question 7

What are the THREE types of Botulism/Botulinum toxin transmission (name and description)?

Answer 7

1. Botulism food poisoning - results from eating food that contains preformed toxin in spore form (most commonly from home canning).
2. Wound Botulism - When the toxin is produced by C. Botulinum organisms contaminating traumatic wounds (eg transfer of contaminated dirt on battlefield into wound).
3. Infant Botulism - is due to a toxin produced by C. Botulinum within the GI tract of infants (can happen from ingesting honey, which may harbor spores).

Question 8

How prevalent is Botulism poisoning/infection?

Answer 8

Around 150 cases a year in the U.S. 65% are the infant, 15% are foodborne. It’s rare in general…

Question 9

How many Botulinum toxin serotypes exist? How are they categorized?

Answer 9

There are EIGHT, categorized A-H.

Question 10

How many serotypes of Botulinum toxin can one strain produce?

Bonus: what are the most common serotypes that affect humans?

Answer 10

Only one.

Bonus: Serotypes A, B, and E most commonly produce disease in humans.

Question 11

What is the best method for destroying Clostridia spores?

Answer 11

Heat at >100 C for at least 10 minutes

Heat completely destroys the toxin

(spores are heat RESISTANT - not heat-PROOF)

Question 12

What are the two components to the Botulinum toxin, and what do they do?

Answer 12

• “A” subunit: is catalytic and cleaves synaptobrevin, syntaxin, and/or SNAP-25. These are components of the SNARE complex, which normally facilitate vesicular exocytosis.
• “B” subunit: binds to the presynaptic receptor at the NMJ, allowing the toxin to be engulfed by the presynaptic cell’s vesicles.

Question 13

Describe common scenarios for food poisoning, from contamination to manifestation of symptoms.

Answer 13

1. Spores of C.B. contaminate spiced, smoked, vacuum packed or canned foods;
2. At alkaline pH, spores germinate into the rods. Under anaerobic conditions, vegetative forms grow and produce toxin;
3. Toxin is absorbed from the stomach and small bowel, and the digestive enzymes do not destroy the toxin = Neurotoxicity.

Question 14

What are the clinical manifestations for Botulism food poisoning?

Answer 14

• Onset 12-36 hours after ingestion;
• Dry mouth, difficulty swallowing, visual disturbances, speech difficulties, descending paralysis (You can distinguish this from a stroke because the patient will be able to understand what is going on)
• Fever not typically seen. GI symptoms often not seen but if they do occur, its most likely associated with Type E;
• High mortality rate due to respiratory paralysis and cardiac arrest.

Question 15

Describe the laboratory test process that confirms the diagnosis of Botulinum toxin poisoning.

Hint: a mouse-model is used.

Answer 15

• Demonstration of toxin in serum or leftover food (or feces/gut content in infant botulism).
• Mice are injected intraperitoneally with sera, feces, or food samples.
• Mice succumb to infection.
• Toxin serotype is identified by neutralization with specific antitoxin in mice.

Question 16

How do you treat ADULT patients with Botulinum toxin poisoning?

Answer 16

• Keep them breathing (paralysis often occurs);
• Before the 8th type was discovered, we had a heptavalent anti-toxin developed that was prepared in horses for the seven serotypes A-G;
• Type H is the newest and thus most dangerous because we have no antitoxin yet.

Question 17

How do you treat INFANT patients with Botulinum toxin poisoning?

Answer 17

Administer “babyBIG” - Botulism Immune Globulin Intravenous (Human)

This is made up of human derived botulism antitoxin antibodies for Type A and B (most common that infect infants)

Question 18

In what situation can the Botulinum toxin be BENEFICIAL? Name a few.

Answer 18

In any condition with muscle spasms can be relaxed with injection of botulinum toxin into that muscle.

Migraines, overactive bladders, strabismus (eyes going to sides), strokes, cerebral palsy, cosmetics.

Question 19

What bacterium (genus and species) produces the potent neurotoxin tetanospasmin?

How do you prevent death from this bacterium?

Answer 19

Clostridium tetani - immunize against it!

Tetanospasmin works by blocking nerve signals from your spinal cord to your muscles, causing severe muscle spasms (hence “lock-jaw”)

Question 20

How many antigenic types of Tetanus toxin exist?

How is it produced?

Answer 20

Only one.

It is produced by vegetative cells (germinated cells) and released when they lyse.

Question 21

Where are C. tetani spores found?

Answer 21

In soil and feces and rusty nails. Yuck.

(PS - rusty nails are no joke! http://www.ncbi.nlm.nih.gov/pubmed/16622677)

Question 22

What is tetanospasmin’s mechanism of action?

Answer 22

Cleaves VAMP (aka “synaptobrevin”) and prevents release of the neurotransmitter glycine from INHIBITORY interneurons in the spinal cord.

This leads to increased stimulation of muscle contractions and tetanic spasms.

Question 23

In four steps, describe the pathogenesis of C. tetani.

Answer 23

1. Spores introduced into body by injury skin via puncture wound, cut, burn;
2. Presence of other organisms and necrotic tissue enhance the reversion of spores to the vegetative forms;
3. Bacteria make the toxin and spread through blood stream and lymphatics;
4. Toxin combines avidly with gangliosides, resulting in neurotoxicity.

Question 24

What is the prevalence of tetanus toxin poisoning?

Answer 24

U.S. = <50 cases a year, usually in older adults who are not updated on immunization or were never immunizede in the first place.

More frequently encountered in disadvantaged countries. Neonatal tetanus is serious and often fatal form in those countries.

Question 25

What are the clinical presentations of C. tetani infection/poisoning?

Answer 25

1. Characteristic initial sign of trismus (lockjaw). In severe cases, trismus becomes persistent with a characteristic facial expression, risus sardonicus (“sardonic grin”);
2. Stiffness of the neck, difficulty swallowing, rigidity of the abdominal muscles;
3. Gradual involvement of other voluntary (skeletal) muscles -tonic spasms;
4. Death usually from interference with mechanics of respiration.

Question 26

How would you treat a patient with C. tetani infection/poisoning?

Answer 26

1. Administer anti-toxin (can’t neutralize what is already bound to nerve tissue), muscle relaxants, sedation, assisted ventilation.
2. Overall, meticulous clinical management is needed for the patient to recover.
3. Immunize

Question 27

Describe FOUR steps that can be taken to prevent C. tetani infection.

Answer 27

1. Active immunization with the toxoid (inactivated form of the toxin);
2. Proper care of the wounds contaminated with soil, etc.;
3. Prophylactic use of the antitoxin called TIG (tetanus immunoglobulin);
4. Administration of metronidazole - inhibits the growth of C. Tetani (bactericidal - specifically inhibits nucleic acid synthesis by causing DNA strand breakage).