Fact sheet on intestinal enterococci in drinking water

General
Intestinal enterococci play an important role in water hygiene. This group of bacteria includes many representatives that are highly relevant as hygiene indicators in water. The occurrence of intestinal enterococci is regarded as an indicator of a faecal contamination that occurred some time ago. Enterococci also belong to the flora of, for example, insects, which can also cause contamination of drinking water.
The Drinking Water Ordinance requires the absence of intestinal enterococci (0 CFU/100 ml). If intestinal enterococci are detected, appropriate countermeasures must be initiated immediately. A positive result for intestinal enterococci in a drinking water sample according to the Drinking Water Ordinance must be reported to the competent authority.

Characteristics

• Coccus-shaped bacteria
• Gram-positive
• Oxidase-negative
• Catalase-negative

Origin / Occurrence

• Widespread in our environment (e.g. soil, plants and surface water)
• Can also be an indicator of insect intrusion

Significance

• Hygiene indicators (for older contaminations)

Important

• Occurrence in hemp fibres, which are often used to seal screw fittings and can lead to contamination if used improperly.
• Have a long survival capability in deposits and biofilms

Growth conditions

• Temperature:
  • Optimum: generally at +30 °C to +37 °C
  • Minimum: usually +7 °C (depending on the species, exceptions even down to 0 °C)
  • Generally no growth above +50 °C
• pH value: growth at 5.5 to 9.0 (depending on the species, exceptions even down to pH 4.4)
• a_w (water activity): growth at high water activity of at least 0.95
• Oxygen requirement: growth with and without oxygen (facultative anaerobe)

Inactivation by heating

• At +72 °C for at least 2 minutes exposure time vegetative bacteria are killed (Note: monitor core temperature)

1. If aerator present: remove and disinfect. Replace depending on condition
2. Remove contaminations and/or biofilms
3. If possible, flame the final section of the water outlet after cleaning
4. Check effectiveness by follow-up testing

1. Possibly perform staged investigations to better identify the location of the contamination in the piping network
2. Engage a specialist company or building services to determine the cause
3. Perform disinfection
4. Check effectiveness by follow-up testing

For drinking or process water from the piping network (cause: installed components/systems)
Contaminated filters and/or water treatment systems in the building installation (e.g. water softening and conditioning systems, filter, distillation, UV systems)

1. Thorough visual inspection of the treatment system
2. Check maintenance intervals, possibly replace filters
3. Engage a specialist company or building services for inspection/maintenance
4. Check effectiveness by follow-up testing

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

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

Contamination after heavy rain (contamination by surface water)

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

1. Thorough visual inspection of the spring collection/well chamber and surrounding area
2. Regular checks of the private water supply system, especially after possible weather-related influences (heavy rain, long dry periods)
3. Carry out the periodic checks required by the health authority
4. Engage a specialist company at appropriate intervals for cleaning and disinfection of the spring collection/well chamber
5. Check effectiveness by follow-up testing

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

in the machine including utensils
or

in the connection hose (supply water)
or

in the piping network (building installation)

1. Thorough visual inspection of machines and connection hoses. This usually also requires disassembling parts of the machines
2. Remove contaminations 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 connection hose between machine and piping network
6. Replace contaminated connection hoses or hoses in poor condition (e.g. brittle, porous) immediately
7. Test the drinking water from the piping network (before the inlet to the machine)
8. Check effectiveness by follow-up testing

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

in the water dispenser
or

in the connection hose (supply water)
or

in the piping network (building installation)

1. Thorough visual inspection of the water dispenser including the connection hose
2. Remove contaminations or biofilms
3. Thorough cleaning and disinfection of the water dispenser (usually by a specialist company)
4. Possibly regularly replace the connection hose between machine and piping network
5. Replace contaminated connection hoses or hoses in poor condition (e.g. brittle, porous) immediately
6. Test the drinking water from the piping network (before the inlet to the water dispenser)
7. Check effectiveness by follow-up testing