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E. coli confirmation and phylogrouping

Most waterborne pathogens are introduced into drinking water supplies via contamination with human or animal faeces. These pathogens cause a range of conditions from mild to severe gastroenteritis, diarrhoea, dysentery, hepatitis and cholera.

Thermotolerant coliforms (faecal coliforms) are always present in high numbers in human and animal faeces. E. coli is the most common thermotolerant coliform present in faeces (typically >90 per cent) and is regarded as the most specific indication of recent faecal contamination. While most thermotolerant coliforms are non-pathogenic, there are some pathogenic subspecies of E. coli that can cause gastrointestinal illness.

E. coli (or thermotolerant coliforms) should not be detected in a minimum 100mL sample of drinking water. If detected, immediate action should be taken as it is an indication of faecal contamination as it suggests that water quality may have been seriously compromised.

However, routine water quality tests (e.g. Colilert) do not provide information on E. coli origin. This information is particularly important when the identification of specific E. coli strains will determine the risk profile and water treatment options used by a water utility.

Phylogrouping enables us to determine if the source of contamination is of animal or environmental origin, which will inform your risk assessment process and water quality management actions.

Escherichia coli strains can be separated into a phylogroup structure, which at present includes eight phylo-groups: A, B1, B2, C, D, E, F and cryptic clade I (Clermont et al., 2013).

Phylogroup B1 strains are the group most often detected in water samples and are considered ‘environmental’ strains. By contrast B2 and D strains are usually detected in human gut flora.

The A0 phylogroup is carried by birds, reptiles, fish and some mammals.

The B1 phylogroup is predominantly environmental.

The risk of this type of E. coli to human health is low.

The B2-3 phylogroup is predominantly carried by humans. The risk of this type of E. coli to human health is high as it may indicate a human faecal contamination event and thus the potential for human infective pathogens to also be present.

The D1 phylogroup is associated with mammalianomnivores, which can include humans and other animals like pigs.

The E phylogroup is associated with herbivores and cattle. The risk of this type of E. coli to human health is medium, there is a possibility that human infective pathogens may also be present.

E. coli risk ratings guide.

E. coli risk ratings guide.