Fact sheet on Clostridium botulinum

General
Clostridia are spore-forming bacteria that can only multiply in the absence of oxygen. Their spores survive under aerobic conditions, high temperatures and drying. Therefore, clostridia and their spores are frequently found in foods.
Sulfite-reducing clostridia include many representatives that play a role as spoilage organisms in foods. One representative of this group is Clostridium botulinum (C. botulinum). Some C. botulinum strains produce neurotoxins that can cause severe foodborne illnesses with paralytic symptoms (botulism). The disease is rare but is associated with a high fatality rate.
The pathogen can also cause the specific clinical picture of infant botulism and wound infections (wound botulism).

• More specific information on clostridia can be found in the fact sheet on sulfite-reducing clostridia and Clostridium perfringens
  

Characteristics

• Rod-shaped bacteria
• Gram-positive
• Oxidase-negative
• Catalase-negative
• Spore-forming
• Toxin-producing

Origin / Occurrence

• C. botulinum and its spores occur in our environment (e.g. soil, sediments of rivers and lakes, standing or slow-flowing waters, mammals, birds and fish)
  
• In improperly produced canned foods as well as in smoked and vacuum-packed foods

Significance

• The heat-resistant spores of C. botulinum can germinate under anaerobic conditions and subsequently produce dangerous toxins in foods. Toxin production by some clostridial strains is even possible at refrigeration temperatures
  
• The botulinum neurotoxin (BoNT) is among the most potent natural toxins
• Foods contaminated with organisms, spores or toxins are usually not detectable or perceptible, except in the case of visible gas formation and bulging containers
• Botulism from commercially produced canned foods practically no longer occurs. However, homemade preserves, smoked and vacuum-packed fish and meat products are still causes of disease

Clinical picture Clostridium botulinum

• Oral ingestion of botulinum neurotoxins (toxin types: A, B, E and F) via food can lead to life-threatening botulism
• In infants (< 1 year) disease can also result from oral ingestion of spores (infant botulism). The spores can germinate in the intestine and produce toxins there. Risk food for infants: honey
• Minimal intoxication dose: 1 to 2 ng toxin per kg body weight is already sufficient to cause severe disease. Few C. botulinum cells can be sufficient
• Incubation period: usually 12 to 72 hours
• Symptoms: nausea, vomiting, gastrointestinal disturbances, difficulty swallowing, dry mouth, signs of paralysis, paralysis of the eye muscles, limbs and swallowing muscles, up to respiratory paralysis with fatal outcome
• Case fatality rate is 10 to 50% (depending on the toxin type, highest mortality with toxin type A)

Examples of affected foods

• Low-acid canned foods, especially homemade meat, fish and vegetable preserves
• Meat products, e.g. improperly cured cooked ham
• Vacuum-packed smoked fish
• Honey

Growth conditions and toxin production

• Temperature
  • Optimum: +35 °C to +40 °C (depending on the C. botulinum strain)
  • Minimum: +4 °C
  • Generally no growth above +58 °C
• pH: growth at pH 4.5 to 8.0
• a_w value: growth at a water activity of at least 0.93
• Oxygen requirement: strictly anaerobic
• Toxin production: under anaerobic conditions and suitable growth conditions

Inactivation by heat

• At +72 °C for at least 2 minutes of exposure time vegetative cells are killed (Note: monitor core temperature)
  • The spores of most clostridial strains are heat-resistant
• Heat-stable spores even survive cooking processes (killing at +121 °C for 3 minutes)
• The botulinum neurotoxins are inactivated from +80 °C

1. Check processes, production protocols and documentation
2. Killing of vegetative bacteria at a core temperature of +72 °C for at least 2 minutes and of heat-resistant spores at +121 °C for 3 minutes. Inactivation of the relatively heat-labile enterotoxins from +80 °C
3. Verify correctness of processes and temperatures
   1. In general, holding temperatures above +60 °C are required
   2. Rapid cooling: within 3 hours a core temperature of at least +7 °C must be reached (special caution required for large quantities)
4. Verification by follow-up testing

1. Check products on receipt for e.g. incoming/transport temperature, shelf life, packaging, deviations or abnormalities
2. This also applies to goods before use in production. When in doubt, do not use the food and consult your supervisor
3. Check microbiological specifications. If necessary, arrange laboratory testing of suspicious products or request results from the supplier
4. Verification by follow-up testing

1. Check products on receipt for e.g. incoming/transport temperature, shelf life, packaging, deviations or abnormalities
2. This also applies to goods before use in production. When in doubt, do not use the food and consult your supervisor
3. Check microbiological specifications. If necessary, arrange laboratory testing of suspicious products or request results from the supplier
4. Verification by follow-up testing

1. Check how cleaning and disinfection are performed:
   1. Hygiene plan
   2. Execution of cleaning and disinfection e.g. disinfectant dosing, contact time, use of suitable and clean materials and cleaning cloths
2. Avoid residual moisture and biofilms. Ensure good drying of equipment, utensils and surfaces
3. Train employees regarding potential errors and corrective measures
4. Repeat cleaning and disinfection
5. Verification by visual on-site inspections, environmental sampling and follow-up testing

1. Check how cleaning and disinfection are performed:
   1. Hygiene plan
   2. Execution of cleaning and disinfection e.g. disinfectant dosing, contact time, use of suitable and clean materials and cleaning cloths
2. Avoid residual moisture and biofilms. Ensure good drying of equipment, utensils and surfaces
3. Train employees regarding potential errors and corrective measures
4. Repeat cleaning and disinfection
5. Verification by visual on-site inspections, environmental sampling and follow-up testing