Botulism is a rare but serious paralytic illness caused by a nerve toxin produced by the bacterium Clostridium botulinum. Botulism toxin is one of the most potent toxins known to humankind – a microgram is lethal to humans. However, there are several ways to inactivate or kill botulism toxin so that it is no longer dangerous.
What is botulism?
Botulism is a potentially fatal illness caused by a nerve toxin produced by Clostridium botulinum bacteria. This bacterium is found in soil and requires an anaerobic (low oxygen) environment to grow and produce toxin. Illness occurs when the toxin is ingested into the body.
There are three main types of botulism:
- Foodborne botulism – caused by eating foods containing the botulism toxin
- Wound botulism – caused by toxin produced from a wound infected with Clostridium botulinum
- Infant botulism – caused by ingesting C. botulinum spores, which then grow and release toxin in the body
All forms of botulism are characterized by paralysis that starts in the muscles of the face and progresses downwards. It is a medical emergency that requires rapid treatment with antitoxin and intensive care.
How does botulism toxin work?
Botulism toxin, also known as Botox, works by blocking nerve impulses to the muscles. It binds to nerve endings and prevents the release of a neurotransmitter called acetylcholine. Without acetylcholine, the muscles are unable to contract, leading to paralysis.
Botulism toxin is extremely potent – it is one of the most toxic substances known. An estimated lethal dose in humans is 1-3 ng/kg when injected or inhaled, and 70 ng/kg when ingested orally. For comparison, cyanide has an oral lethal dose of 100-200 mg/kg. The botulinum toxin molecule is quickly taken up into nerve cells after entering the body.
What factors inactivate or kill botulism toxin?
Although botulism toxin is extremely potent, there are several factors that can inactivate or kill the toxin molecule:
Heat
Heating food or liquids to high temperatures can denature and inactivate botulism toxin. Studies have found botulism toxin becomes inactivated at temperatures above 80°C (176°F). Toxin activity rapidly decreases as temperature rises above this point. Pressure canning low-acid foods at 116°C (240°F) for the recommended time has been shown to effectively destroy any botulism toxin that may be present.
High acidity
Botulism toxin can be inactivated by high acidity levels. Toxin exposed to pH levels below 4.6 for 10 minutes at room temperature has been shown to be completely inactivated in food. This is why botulism from canned goods is mainly a concern with low acid foods, such as meat, vegetables and fish stored in oil. The high acidity of fruits prevents growth and toxin production of C. botulinum bacteria.
Oxidizing chemicals
Oxidizing agents such as chlorine bleach, hydrogen peroxide, peracetic acid and nitrites can irreversibly inactivate botulism toxin by oxidizing key amino acids in the protein structure. This damages the toxin molecule so it can no longer bind to nerve cells. Chemical disinfectants containing these oxidizers are able to neutralize botulism toxin contamination.
Radiation
Ionizing radiation has been shown to degrade and inactivate botulism toxin by damaging the protein structure. Gamma irradiation from Cobalt-60 or electron beam radiation can be used to sterilize and detoxify food contaminated by C. botulinum. Radiation doses above 20 kGy result in complete inactivation of botulism toxin.
Antitoxins
Antitoxins provide passive immunity against botulism toxin. They contain antibodies that bind to and neutralize the toxin molecules. Antitoxins do not reverse paralysis but can prevent progression if administered early. There are antitoxins available for infant botulism (BabyBIG) and for adult intestinal toxemia botulism.
How is botulism toxin inactivated in food?
Since foodborne botulism arises from consuming foods containing botulism toxin, inactivation of the toxin in food is crucial for prevention. The food industry uses various processing methods to ensure botulism toxin is deactivated inside canned or packaged foods:
- Thermal processing – Low acid foods are heated to 121°C (250°F) for a certain time period to destroy C. botulinum spores and inactivate any toxin present.
- pH control – Acid foods like fruits and pickles are kept at a pH below 4.6 to prevent growth and toxin production.
- Water activity – Dehydrating or adding salt/sugar lowers water activity below 0.85, inhibiting growth of C. botulinum.
- Nitrites and nitrates – These preservatives inhibit growth of C. botulinum and can inactivate its toxins.
- High pressure processing – Exposing food to pressures above 600 MPa can inactivate spores and toxin.
These processing methods are designed to destroy any botulism toxin that could be produced by C. botulinum bacteria that manages to survive and grow in the food during storage and distribution.
Can botulism toxin be inactivated after food processing?
If food already contaminated with botulism toxin is identified, steps can be taken to try and inactivate the toxin after the food has been processed and packaged:
Boiling
Bringing foods like canned vegetables, soups and meats to a rolling boil for 10 minutes or longer can denature and inactivate botulism toxin. The food must be stirred occasionally to ensure the boil reaches all areas.
Irradiation
Exposing contaminated food to ionizing radiation sources like gamma rays or electron beams (>=20 kGy) has been shown to deactivate botulism toxin by damaging its molecular structure.
Discarding
If uncertain about the safety of a food after post-processing attempts to inactivate botulism toxin, it is best to be cautious and dispose of the food. Botulism is extremely dangerous with a high fatality rate if untreated. When in doubt, it is safer to throw it out.
Conclusion
Botulism toxin is a potent neurotoxin but can be neutralized by various treatments that damage its molecular structure. Heating foods to high temperatures, irradiating with gamma rays, or exposing the toxin to oxidizing chemicals, high acidity or high pressures can all inactivate botulism toxin. Proper thermal processing and food preservation techniques are used by the food industry to eliminate the possibility of botulism toxin entering canned/packaged foods. However, if contamination is discovered after processing, further steps like boiling or irradiation may be necessary to deactivate any remaining botulism toxin and render the food safe for consumption.