Fact sheet on Clostridium perfringens in drinking water

General
Clostridium perfringens belongs to the genus Clostridia, which are spore-forming bacteria. The spore as a dormant form is very resistant to disinfectants and can persist for long periods. Active bacteria can develop again from the spore. Clostridia are widespread in the environment.
The Drinking Water Ordinance requires the absence of Clostridium perfringens (0 CFU/100 ml). If a positive result for Clostridium perfringens is obtained, appropriate countermeasures must be initiated immediately. A positive finding of Clostridium perfringens in a drinking water sample according to the Drinking Water Ordinance must be reported to the competent authority.

Characteristics

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

Origin / Occurrence

• These bacteria and their spores are widespread in our environment (e.g., soil, dust, water, intestinal tract of animals and humans)

Significance

• Indicator of contamination, e.g., by surface water or soil
• When ingested orally, pathogenic C. perfringens strains can produce enterotoxins and release them during sporulation in the intestine

Clinical picture

• Minimum intoxication dose: typically 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 due to enterotoxins: diarrhea with abdominal pain
• Complications: rare

Growth conditions and toxin production

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

Inactivation by heat

• Exposure at +72 °C for at least 2 minutes will kill vegetative bacteria (note: check core temperature) → spores are usually heat-resistant
• Heat-resistant spores can even survive boiling processes (inactivation at +100 °C for at least 60 minutes)
• The C. perfringens enterotoxin, which is released only in the intestine, is relatively heat-sensitive. Inactivation at +60 °C in 5 minutes

1. If an aerator is present: remove and disinfect. Replace depending on condition
2. Remove contamination and/or biofilms
3. If possible, flame-sterilize the last section of the water outlet after cleaning
4. Follow-up testing to verify effectiveness

1. If necessary, carry out stepwise investigations to better identify the point of contamination in the piping network
2. Engage a specialist company or building services (facility management) to determine the cause
3. Perform disinfection
4. Follow-up testing to verify effectiveness

1. Thorough visual inspection of the treatment system
2. Check maintenance intervals; replace filters if necessary
3. Engage a specialist company or building services for inspection/maintenance
4. Follow-up testing to verify effectiveness

For drinking water from private water supply systems, i.e., from private wells and springs

Contamination due to intervention/repair in the spring/well chamber

Contamination after heavy rainfall (contamination from surface water)

Contamination due to construction defects in the spring/well chamber (leakage, age-related wear)

1. Thorough visual inspection of the spring/well chamber and surrounding area
2. Regular inspection of the private water supply system, especially after weather-related events (heavy rain, prolonged drought)
3. Carry out the periodic inspections required by the health authority
4. Engage a specialist company at appropriate intervals to clean and disinfect the spring/well chamber
5. Follow-up testing to verify effectiveness

For flake ice, crushed ice and ice cubes
Hygienic deficiencies:

in the machine including utensils
or

in the connecting hose (supply water)
or

in the piping network (building installation)

1. Thorough visual inspection of machines and connecting hoses. This usually requires disassembling parts of the machines
2. Remove contamination or biofilms
3. Thorough cleaning and disinfection of machines and components (possibly by a specialist company)
4. Thorough cleaning and disinfection of utensils (e.g., scoop)
5. Regularly replace the connecting hose between machine and piping network
6. Replace contaminated connecting hoses or hoses in poor condition (e.g., brittle, porous) immediately
7. Test the drinking water from the piping network (before it enters the machine)
8. Follow-up testing to verify effectiveness

Water dispensers connected to the piping network (building installation)
Hygienic deficiencies:

in the water dispenser
or

in the connecting hose (supply water) 
or

in the piping network (building installation)

1. Thorough visual inspection of the water dispenser including connecting hose
2. Remove contamination or biofilms
3. Thorough cleaning and disinfection of the water dispenser (usually by a specialist company)
4. Possibly replace the connecting hose between machine and piping network at regular intervals
5. Replace contaminated connecting hoses or hoses in poor condition (e.g., brittle, porous) immediately
6. Test the drinking water from the piping network (before it enters the water dispenser)
7. Follow-up testing to verify effectiveness