Bacterial Food Intoxication: A Look at Botulism

Botulism is a type of food poisoning that is caused by the bacteria Clostridium Botulinum. This particular bacteria grows is an obligate anaerobe, which means that the bacteria grow in an environment that lacks oxygen (such as in a sealed home-canning jar.) Clostridium Botulinum produces endospores that allow the bacteria to go into a dormant state in the lack of available nutrients; when conditions are ideal to grow again, the endospore germinates, and the bacteria continue to replicate. It is a gram positive bacillus, easily seen on a microbiological Gram stain. Botulism is currently considered the most dangerous food-borne intoxication, and will be fatal if not treated early. The dangerous nature of botulism doesn't stem from ingesting the bacteria itself, but rather from the exotoxin that the Clostridium Botulinum releases. This extotoxin attacks the person's nervous system, causing flaccid paralysis.

In a normal muscle cell, there is a space between the muscle cell and the neuron that transmits signals from the brain. That space is called the synaptic cleft. To work properly, there are small vesicles filled with acetylcholine contained in the neuron; those vesicles attach to the cytoplasmic membrane of the neuron. When this occurs, the acetylcholine is released into the synaptic cleft where it crosses over to the muscle cell. This carries the information that the muscle cell needs to tell it to contract, or move. When the botulism is present, the toxin binds permanently to the neuron cytoplasmic membrane, thus blocking the release and transmission of the acetylcholine. The muscle cells will no longer be able to contract without that signal, and so the affected person's muscles appear limp and flaccid.

Botulism fatalities occur quickly; often death occurs within 1 to 2 days of symptom onset. Death is caused by respiratory paralysis- in other words, the person suffocates to death. If the diagnosis of botulism is made early however, treatment can be given in the form of antitoxins. Time is of the essence however, as there are seven identified forms of botulism, and the specific antitoxin therapy must be given. The antitoxins neutralize the unbound toxins before they can bind to the neurons, but often life support systems (such as ventilators) are still utilized. Complete recovery can take up to a year.

A common cause of botulism is home canning foods that have a low acid content such as green beans, corn and beets. The risk is increased if the foods are then consumed cold, as the toxin is destroyed by exposure to temperatures of 194 degrees Fahrenheit for 10 minutes. Understanding risk factors, and being sure to eliminate those risks are a key in avoiding this deadly bacterial toxin.

Source: Dr. Jeffrey C. Pommerville, Alcamo's Fundamentals of Microbiology.