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Clostridium botulinum (Botulism)





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Clostridium botulinum (Botulism)


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High Yield Notes
9 pages

Clostridium botulinum (Botulism)

24 flashcards

USMLE® Step 1 style questions USMLE

2 questions

A 4-month-old boy presents to the emergency department with weakness and difficulty feeding. Parents state the patient has been getting progressively weaker over the past two days. The parents state, “He is not crying as loudly as he used to, and he has not had a bowel movement recently either.” Prior to this, the patient has been developing normally and had no issues during gestation or birth. Vital signs are within normal limits. Physical examination shows global hypotonia and drooling from the mouth.  Which of the following best describes the most likely source of this patient’s clinical presentation?  

External References

Clostridia, as a family, are obligate anaerobes, meaning that oxygen is toxic to them.

In nature, they thrive in deep, compact soil, and when they feel the stress of fresh oxygenated air, they often produce spores, which are metabolically inert and extremely resilient to the environment.

Then, when environmental conditions improve, the spores are able to sprout into fully fledged Clostridia.

When doing a Gram stain, Clostridium botulinum stains purple, or Gram positive, and it’s a bacillus, meaning that it looks like a big cylinder or rod under the microscope.

Clostridium botulinum is notorious for producing a toxin, called botulinum toxin, which causes botulism.

Historically, to preserve foods, processes like sausage making and canning became popular.

Unfortunately, since these environments block out air, if a Clostridium botulinum spore gets in during the food preparation process, it can grow and produce botulinum toxin, contaminating the food.

In fact, this is how Clostridium botulinum gets its name, since botulus means sausage in Latin.

When it infects a can, the can begins to bulge with air because the bacteria metabolized sugars into short chain fatty acids that form a gas.

And although the short chain fatty acids are mostly made up of carbon dioxide and hydrogen, the gas is particularly foul smelling.

Now, nerves that use the neurotransmitter acetylcholine are those we use for muscle control.

Upon ingesting a contaminated food product, botulinum toxin works by binding specifically to these nerves, inhibiting muscle contraction.

The toxin comes in eight distinct types, named type A, B, C, D, E, F, G, and H, and they vary in their toxicity.

The neuron takes in the botulinum toxin by endocytosis, creating a small vesicle that floats within the neuron’s cytoplasm.

The toxin then activates and slips out of the vesicle, and starts to cleave SNARE proteins.

SNARE proteins tug vesicles containing acetylcholine to the plasma membrane, where they get released into the synapse, and transmit a signal to the muscle.

Without SNARE proteins, acetylcholine doesn’t get released, and no signal is sent out by the affected nerves.

The result is that muscles get completely relaxed and flaccid.

Muscle weakness usually starts in the muscles supplied by the twelve cranial nerves - so, the muscles that control the face, eye movements, chewing and swallowing.

In addition, nerves of the autonomic nervous system that rely on acetylcholine are also affected.

Early on, botulism can cause a bulbar palsy, or impairment of cranial nerves IX, X, XI and XII, and over time there may be a descending paralysis.


Clostridium botulinum is a gram-positive, rod-shaped, anaerobe, spore-forming bacterium known to produce botulinum toxin, which causes botulism. Botulism can happen after eating food contaminated with the toxin or by breathing in the toxin. The symptoms of botulism include weakness, dizziness, double vision, drooping of the eyelids, trouble speaking or swallowing, and muscle paralysis. If it's not quickly treated, botulism can lead to death.