AssessmentsClostridium botulinum (Botulism)
Clostridium botulinum (Botulism)
USMLE® Step 1 style questions USMLE
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?
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.
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.
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.
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.
In addition, nerves of the autonomic nervous system that rely on acetylcholine are also affected.