Fact sheet on sulfite-reducing clostridia and Clostridium perfringens

General information
Clostridia are a genus of spore-forming bacteria that can only multiply in the absence of oxygen (strict anaerobes). However, the spores can survive under aerobic conditions, at high temperatures (e.g. heating steps) and during drying. Clostridia and their spores are widespread in the environment, which is why they regularly occur in foods.

The group of sulfite-reducing clostridia play a role in foods primarily as spoilage organisms. Pathogens such as Clostridium perfringens (C. perfringens) and Clostridium botulinum (C. botulinum) are also included in this group of bacteria.

→ More specific information on Clostridium botulinum is available in a separate fact sheet

Characteristics

• Rod-shaped bacteria
• Gram-positive
• Oxidase-negative
• Catalase-negative
• Spore-formers
• Toxin producers (Clostridium perfringens)

Origin / Occurrence

• These bacteria and their spores are widespread in our environment (e.g. soil, dust, water, gastrointestinal tract of animals and humans)
• Present in plant- and animal-based foods

Significance

• The group of sulfite-reducing clostridia are regarded in foods as spoilage organisms. However, there are also potentially pathogenic species among them such as C. perfringens and C. botulinum
• C. perfringens is particularly known as a cause of foodborne outbreaks in catering and communal feeding. Spores germinate in the food after cooking and then multiply if holding temperatures are too low or cooling is too slow
• Pathogenic C. perfringens strains produce enterotoxins and release these mainly during sporulation in the intestine

Clinical picture Clostridium perfringens

• Minimum toxic dose: generally at least 10⁵ CFU/g (when enterotoxin is produced)
• Incubation period: 8 to 20 hours
• Duration of illness: usually 10 to 24 hours
• Symptoms of intoxication by enterotoxins: diarrhea with abdominal pain
• Complications are rare

Examples of affected foods

• Meat dishes with large pieces of meat; roasts
• Soups, sauces (especially in large containers)
• Vacuum-packed meat and fish products
• Poultry and meat salads

Growth conditions and toxin production

• Temperature:
  • Optimum: +43 °C to +47 °C
  • Minimum: +15 °C (depending on the clostridial strain, exceptions even down to +4 °C)
  • Generally no growth above +58 °C
• pH: growth at pH 5.0 to 8.0
• a_w value: growth at a water activity of at least 0.94
• Oxygen requirement: (strictly) anaerobic (spores also survive in the absence of oxygen)
• Toxin production: dependent on the clostridial strain, generally under optimal growth conditions

Inactivation by heating

• Vegetative bacteria are killed at +72 °C for at least 2 minutes (Note: check core temperature) → spores are heat-stable, however
• Heat-resistant spores can even survive cooking processes (inactivation requires +100 °C for at least 60 minutes)
• The C. perfringens enterotoxin, which is released only in the intestine, is relatively heat-sensitive. Inactivated at +60 °C in 5 minutes

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 heat-resistant spores at +100 °C for at least 60 minutes. Inactivation of heat-labile enterotoxins at +60 °C for 5 minutes
3. Check correctness of processes and temperatures
   1. In general, holding temperatures above +60 °C are required
   2. Rapid cooling: after 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. Demand traceability of the cold chain during transport from the supplier
2. Check incoming and storage temperatures
3. Monitor refrigeration temperatures and cold chains during processing, transport and sale
4. If overage (i.e., excessively long shelf life) is suspected, carry out appropriate storage tests
5. Verification by follow-up testing

1. Check incoming goods for e.g. incoming/transport temperature, shelf life, packaging, deviations or irregularities
2. The same applies to goods before use in production. If in doubt, do not use the food and consult a 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 the execution of cleaning and disinfection:
   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, devices and surfaces
3. Train staff regarding potential errors and corrective measures
4. Repeat cleaning and disinfection
5. Verification by visual on-site inspections, environmental sampling and follow-up testing