Clostridium botulinum is a Gram-positive, anaerobic, rod-shaped bacterium that produces toxins (in particular neurotoxins), which cause the serious disease botulism. The bacteria are found in a variety of environmental sources such as soil, coastal waters and lakes, inside the gills of shellfish and within the intestinal tracts of mammals and fish. C. botulinum thrives in conditions where there are low levels of oxygen which enable them to produce endospores. These heat-resistant spores remain dormant until they are activated by an external change in their conditions which causes them to multiply and release toxins into the host.
There are seven strains of C. botulinum: A, B, C, D, E, F and G, which are defined by the specificity of their toxins, and which cause botulism in humans and animals.
- Strains A, B, E and F cause human botulism
- Strains C and E cause avian botulism
- Strains C and D are responsible for botulism in animals such as cattle, horses, chickens and several species of fish
- There are no recorded outbreaks of Type G botulism.
Neurotoxin strains A and B are commonly used as motor nerve blocker to treat certain eye conditions, e.g. blepharospasm (twitching) and strabismus (squinting); they are also used in cosmetic procedures such as Botox where they are injected into facial muscles to prevent further wrinkling.
Most C. botulinum strains produce a single toxin but there have been reports of strains which have the capability to produce two or more toxins. C. botulinum bacteria can lead to botulism in four different forms:
- Foodborne: develops when foods are consumed which are contaminated with the botulinum toxin
- Infant: develops when infected botulinum spores grow and produce toxin within the child’s intestinal tract
- Wound: a rare form of botulism which occurs when a wound is infected with C. botulinum, producing toxins which spread throughout the body
- Adult intestinal toxaemia: an uncategorised form of botulism in adults which occurs when C. botulinum spores invade the intestinal tract, releasing toxin in vivo.
Infants exhibit muscle weakness, breathing difficulties, poor muscle tone, constipation and lethargy. Adults experience blurred vision, double vision and slurred speech, difficulties with swallowing, dry mouth, lethargy and muscle weakness. Without treatment these symptoms will worsen, leading to paralysis of the motor and respiratory systems, which can be fatal.
Although cases of botulism are rare, mortality is high. From 1990 to 2000, there were 263 cases of food-borne botulism in the US, an annual incidence of 0.1 per million.
Only a few nanograms of toxin is needed to cause illness.
C. botulinum bacteria are found in a variety of home/commercial tinned foods which have been inadequately processed, thereby allowing the bacteria to grow and produce neurotoxin. These foods include tinned vegetables, meats, sausages and fish, herb-infused oils and bottled garlic. Spores can also be found in honey and other sweeteners although they do not thrive in a highly concentrated sugar solution. However, they do grow in a low oxygen, low acid environment such as a baby’s large intestine. The large intestine is a ripe breeding ground for spore germination and the production of toxins which cause infant botulism. As a result of this, honey should not be given to infants under 12 months old.
- United States Food and Drug Administration. Bad Bug Book: Foodborne pathogenic microorganisms and natural toxins handbook
- Food Safety.gov
- Centers for Disease Control and Prevention. Botulism
- Bellaire Neurology: how Botox works
Image shows chemical structure of a botulinum toxin molecule.
Learn more about other common and less common food bugs in our series of Thermo Scientific Application Notes, some of which are available to download as PDFs. Alternately, visit our food document library.