Clostridium botulinum

Clostridium botulinum is a bacterium that produces the toxin botulin, the causative agent in botulism.^[1] It is included in the genus Clostridium, a major group of Gram-positive forms. C. botulinum was first recognized and isolated in 1896 by Emile van Ermengem and is commonly found in soil.

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These rod-shaped organisms grow best in low-oxygen conditions. They form spores that allow them to survive in a dormant state until exposed to conditions that can support their growth.^[2]

Subtypes

Each of the seven subtypes of C. botulinum produces a different botulin toxin.^[3] These are labeled with letters and are called A to G types. Types C and D are not human pathogens. A "mouse protection" test determines the type of C. botulinum present using monoclonal antibodies.

In the United States, outbreaks are primarily due to types A or B, which are found in soil, or type E, which is found in fish. Optimum temperature for types A and B is 35-40 °C. Minimum pH is 4.6. It takes 25 min at 100 °C to kill these types. Optimum temperature for type E is 18-25 °C. Minimum pH is 5.0. It takes about 0.1 minute at 100 °C to kill type E C. botulinum.

C. botulinum strains that do not produce a botulin toxin are referred to as Clostridium sporogenes.^[4] The species are otherwise phylogenetically indistinguishable, and C. sporogenes is often used as a model for the toxic subtypes.

Clostridium botulinum is also used to prepare Botox, used to selectively paralyze muscles to temporarily relieve wrinkles. It has other "off-label" medical purposes, such as treating severe facial pain, such as that caused by trigeminal neuralgia.

Botulin toxin produced by Clostridium botulinum is often believed to be a potential bioweapon as it is so potent that it takes about 75 nanograms to kill a person (LD50 of 1ng/kg,^[5] assuming an average person weighs ~50kg), 500 grams of it would be enough to kill the entire human population (6.6 billion).

Clostridium botulinum is a soil bacterium. The spores can survive in most environments and are very hard to kill. They can survive the temperature of boiling water at sea level, thus many foods are canned with a pressurized boil that achieves an even higher temperature, sufficient to kill the spores.

Growth of the bacterium can be prevented by high acidity, high ratio of dissolved sugar, high levels of oxygen, or very low levels of moisture. For example in a low acid, canned vegetable such as green beans that are not heated hot enough to kill the spores (i.e., a pressurized environment) may provide an oxygen free medium for the spores to grow and produce the toxin. On the other hand, tomatoes or tomato sauce are sufficiently acidic to prevent growth; even if the spores are present, they pose no danger to the consumer. Honey, corn syrup, and other sweeteners may contain spores but the spores cannot grow in a highly concentrated sugar solution; however, when a sweetener is diluted in the low oxygen, low acid digestive system of an infant, the spores can grow and produce toxin. As soon as infants begin eating solid food, the digestive juices become too acidic for the bacterium to grow.

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