Clostridium Botulinum (Botulism)


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much more. Try it free today! 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. Symptoms of botulism include double vision,
drooping of the eyelids, an inability to make any facial expressions, and difficulty swallowing. In addition, because of the autonomic nervous
system affects, it can cause dry mouth, postural hypotension, or low blood pressure while standing,
nausea, vomiting, and constipation. Often, the symptoms of botulism can progress
to complete flaccid paralysis, which can be deadly, if it involves the respiratory muscles. The diagnosis of botulism is primarily based
on a serum analysis for the botulinum toxin. Growing Clostridium botulinum in culture is
rarely successful, because anaerobes are difficult to grow in a lab setting. Treatment of botulism is mostly supportive,
and the goal is to assist the affected patient in breathing. In adults, botulism can also be treated by
passive immunization, with an antitoxin. Two types of antitoxin exist, a trivalent
one which covers toxins A, B, and E, and a heptavalent one, covering toxins A, B, C,
D, E, F, and G. The purpose of antitoxin is to catch the free
toxin molecules in the bloodstream, before they can damage the neuronal proteins. Now, most canning processes undergo high pressure
cooking, which is like autoclaving, and reliably destroys the toxin, and sterilizes the contents
of the can. Other preserved foods can be conserved by
high acidity, or low pH – for example, pickles. The most common form of food related botulism
is infant botulism, or floppy baby syndrome. Newborns and infants still have poorly developed
gut flora, and their gut is vulnerable to colonization by Clostridium botulinum. Colonizing bacteria will continue to produce
their toxins directly in the intestine, causing botulism. Honey had been implicated as a potential vector
for transmitting Clostridium botulinum spores, and should be avoided in children under 12
months. Finally, two types of Botulinum toxin – A
and B – are less toxic, and can reliably induce long lasting neuromuscular junction block,
so they are sometimes diluted and injected into a rigid muscle to relax it. Other diseases that can be improved with botulinum
toxin are hyperhidrosis, or excessive sweating, achalasia, and focal dystonia, which is where
there’s an involuntary spasticity in a muscle group. Botulinum toxin is also used as “botox”
in aesthetic surgery to help smooth out wrinkles for a few months. All right, as a quick recap. Clostridium botulinum is an obligate anaerobe
that makes spores, and secretes a botulinum toxin, which causes botulism. Spores are usually found in badly preserved
food, and honey. Consumption of food contaminated with botulinum
toxin can lead to neuromuscular block, and flaccid paralysis, that may be lethal through
suffocation without supportive treatment.

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