Anaerobic, Gram Positive, spore-forming rods are characteristic features of which bacterial genus?
What does it mean for Clostridia (or any other microbe) to be an "anaerobe"?
It can’t use O2 as a final electron acceptor
What enzyme do strict anaerobes (like Clostridia) LACK? What does this enzyme do?
Superoxide dismutase - this enzyme neutralizes toxic superoxide anions that accumulate in the presence of O2
List SIX medically-relevant agents related to Clostridia.
Hint: this includes toxin(s) and disease(s)
3- Gas gangrene
4- Food poisoning
5- Clostridium difficile-associated disease (CDAD)
6- Pseudomembranous colitis
Describe TWO general features of bacterial spores that make them "hardy", or resistant to destruction
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.
List the three types of spores that Clostridia can form.
Hint: these are based on the spore's location
1- Tetanus (think of tennis rackets)
2- Gas Gangrene Tetanus
What are the THREE types of Botulism/Botulinum toxin transmission (name and description)?
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).
How prevalent is Botulism poisoning/infection?
Around 150 cases a year in the U.S. 65% are the infant, 15% are foodborne. It’s rare in general...
How many Botulinum toxin serotypes exist? How are they categorized?
There are EIGHT, categorized A-H.
How many serotypes of Botulinum toxin can one strain produce?
Bonus: what are the most common serotypes that affect humans?
Bonus: Serotypes A, B, and E most commonly produce disease in humans.
What is the best method for destroying Clostridia spores?
Heat at >100 C for at least 10 minutes
Heat completely destroys the toxin
(spores are heat RESISTANT - not heat-PROOF)
What are the two components to the Botulinum toxin, and what do they do?
- "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.
Describe common scenarios for food poisoning, from contamination to manifestation of symptoms.
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.
What are the clinical manifestations for Botulism food poisoning?
- 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.
Describe the laboratory test process that confirms the diagnosis of Botulinum toxin poisoning.
Hint: a mouse-model is used.
- 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.
How do you treat ADULT patients with Botulinum toxin poisoning?
- 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.
How do you treat INFANT patients with Botulinum toxin poisoning?
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)
In what situation can the Botulinum toxin be BENEFICIAL? Name a few.
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.
What bacterium (genus and species) produces the potent neurotoxin tetanospasmin?
How do you prevent death from this bacterium?
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")
How many antigenic types of Tetanus toxin exist?
How is it produced?
It is produced by vegetative cells (germinated cells) and released when they lyse.
Where are C. tetani spores found?
In soil and feces and rusty nails. Yuck.
(PS - rusty nails are no joke! http://www.ncbi.nlm.nih.gov/pubmed/16622677)
What is tetanospasmin's mechanism of action?
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.
In four steps, describe the pathogenesis of C. tetani.
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.
What is the prevalence of tetanus toxin poisoning?
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.
What are the clinical presentations of C. tetani infection/poisoning?
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.
How would you treat a patient with C. tetani infection/poisoning?
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.
Describe FOUR steps that can be taken to prevent C. tetani infection.
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).