Clostridium botulinum is a ubiquitous organism found in soil, salt, fresh water sediments and the gastrointestinal tracts of animals and fish.
Seven distinct types are recognised. Types A, B and E account for nearly all human cases of foodborne botulism.
The non-proteolytic strains of Clostridium botulinum have a growth range between 3ºC and 45ºC. They will therefore multiply and produce neurotoxin at chill temperatures, albeit slowly.
Their spores can be destroyed in food by an appropriate pasteurisation process, discussed later in this module.
Botulism is a severe illness caused by a neurotoxin from an anaerobic spore-forming bacterium, Clostridium botulinum.
There are three forms of botulism recognised today: foodborne botulism, where toxin is ingested; infant botulism; and wound botulism. The classic illness, and the most common in the UK, is foodborne, which is an intoxication and therefore not an infection.
Foodborne botulism has been reported in many countries throughout the world.
See Table 2: Recorded outbreaks and types involved in foodborne botulism in the 1992 ACMSF report.
Non-proteolytic Clostridium botulinum has the ability to grow at low temperatures. An incubation period of several weeks is generally needed for toxin formation at the lower end of the temperature range. This is the basis for the ACMSF recommendation to restrict shelf-life if no controlling factors can be demonstrated.
The lowest established temperature limit for growth and toxin production by strains of non-proteolytic Clostridium botulinum is 3ºC. The upper limit is in the range 40–45ºC.
The first reported outbreak of botulism in the UK was in 1922 at Loch Maree in Scotland. Eight people died after eating sandwiches made from wild duck pâté.
The largest outbreak of botulism reported in the UK to date was in 1989 and involved hazelnut yoghurt. Information about these and other cases are listed in the table below. There have been no cases associated chilled foods in the UK.
See Table 5: Foodborne botulism in the UK in the 1992 ACMSF report.
Key points:
- Pyschotrophic strains of Clostridium botulinum have a growth range of 3ºC to 45ºC.
- These strains will produce neutrotoxin at chill temperatures.
- The foods most at risk are those in which the spoilage microflora are eliminated while pyschotrophic Clostridium botulinum may survive and grow.