Escherichia coli (E. coli) (pathogenic)

(endorsed 2011)

Guideline

No guideline value has been set for pathogenic Escherichia coli and its inclusion in routine monitoring programs is not recommended.

A multiple barrier approach from catchment to tap is recommended to minimise the risk of contamination. Protecting catchments from human and animal wastes is a priority. Operation of barriers should be monitored to ensure effectiveness and that microbial health-based targets are being met.

General description

Escherichia coli (E. coli) is used as the primary indicator of faecal contamination of drinking-water supplies, due to its prevalence in the gut of warm-blooded animals. Most E. coli are non pathogenic, normal inhabitants of the gut, but there are several types that are pathogens and have been responsible for waterborne disease outbreaks. Pathogenic E. coli are classed into six groups: enterotoxigenic E. coli (ETEC), enterohaemorrhagic E. coli (EHEC) [also known as Shig-toxin producing E. coli STEC], enteroinvasive E. coli (EIEC), enterpathogenic E. coli (EPEC), enteroadherent-aggregative E. coli (EA-AggEC), and diffuse adherent E. coli (DAEC) (Nataro and Kaper 1998, Rice and Degnan 2006).

All strains of pathogenic E. coli other than EHEC have the human gastrointestinal tract as a primary reservoir; EHEC is predominately found in ruminants. Toxigenic E. coli (including O157 and other related strains) are carried by 10-15% of healthy ruminants, including cattle, sheep, goats and deer. In cattle, toxigenic EHEC strains have been found at colonisation rates as high as 60% and typically in the range 10-25% (Nataro and Kaper 1998).

The bacteria may be transmitted to humans by eating raw or undercooked meats, or via foodstuffs or water supplies contaminated with faeces from infected humans or animals. Outbreaks have been attributed to drinking-water supplies as well as recreational water bodies and direct contact with animals. For EHEC, the infectious dose may be as low as 10 to 100 organisms (Teunis et al. 2004).

Australian significance

There have been no reported outbreaks of waterborne disease associated with pathogenic E. coli in Australia. A significant food-borne outbreak of E. coli O111:NM occurred in Adelaide in 1995, associated with the consumption of uncooked semi-dry fermented sausages (Cameron et al. 1995). Twenty-three cases of Haemolytic Uraemic Syndrome (HUS) and a further 30 cases of bloody diarrhoea were reported.

Preventing contamination of drinking water

Protecting source waters from contamination by human and livestock waste will reduce the potential presence of pathogenic E. coli. Like other E. coli strains, they are highly sensitive to disinfection. Distribution systems should be protected from ingress of faecal contamination.

Method of identification and detection

There is no standard method for detection of pathogenic E. coli. They can differ from non-pathogenic E. coli in a number of ways that make traditional detection methods unsuitable. For example, some pathogenic groups, such as EIEC, do not ferment lactose; and EHEC do not ferment sorbitol or rhaminose, or contain beta-glucuronidase and they grow poorly at 44.5°C. Hence defined substrate technologies that rely on beta-glucuronidase activity to detect E. coli will not detect all pathogenic strains.

Standard Methods for the Examination of Water and Wastewater (APHA et al. 2005) describes different methods for EHEC, EPEC, ETEC and EIEC strains. Each of the methods involves initial isolation using standard liquid or agar-based media used for total coliforms, thermotolerant coliforms or Salmonella. Confirmation requires biochemical testing and serotyping. Commercial kits are available for detecting some toxins, including the shiga toxins produced by EHEC.

Health considerations

The most significant pathogenic E. coli for the water industry are the enterohaemorrhagic E. coli (EHEC). EHEC comprise more than 100 different serotypes, including O157:H7, which has been responsible for a number of waterborne disease outbreaks.

EHEC, including serogroups such as O111 and O157, are relatively rare strains which produce large quantities of shiga-like (or vero) toxins that can cause illness ranging from mild diarrhoea to haemorrhagic colitis. Haemorrhagic colitis is characterised by blood-stained diarrhoea accompanied by abdominal pain. In addition, EHEC strains can cause HUS, which is characterised by acute renal failure and haemolytic anaemia. The infectious dose may be very low (Teunis et al. 2004) and the incubation period ranges from 2 to 8 days.

Several waterborne disease outbreaks have been caused by E. coli O157:H7, including the groundwater outbreak in Walkerton, Canada, in May 2000. This outbreak resulted in an estimated 2300 individuals becoming ill, with 65 hospital admissions and 7 deaths. The causal agents were E. coli O157:H7 and Camplyobacter, attributed to manure contamination of the groundwater supply (Hrudey and Hrudey 2004).

Enteropathogenic E. coli (EPEC) have been primarily associated with outbreaks of infantile gastroenteritis, but investigations have shown that they also cause disease in adults (Nataro and Kaper 1998). The pathogenic mechanisms employed by these organisms are not fully understood.

Enteroinvasive E. coli (EIEC) produce dysentery by a mechanism similar to Shigella spp. These organisms invade the colonic mucosa and cause bloody diarrhoea. This property seems to be restricted to a few O serogroups.

Epidemiological evidence suggests that enterotoxigenic E. coli (ETEC) are responsible for most episodes of E. coli diarrhoea, particularly in developing countries. ETEC strains can cause a cholera-like syndrome in infants, children and adults, producing a heat-labile enterotoxin (LT) related to cholera enterotoxin, and/or a heat-stable enterotoxin (ST). The action of LT is the same as the cholera toxin. The ability of ETEC to cause disease depends not only on the production of enterotoxin but also upon the organisms’ ability to colonise the small intestine. Various colonising factors or adhesins have been described.

Derivation of guideline

No guideline value is proposed for pathogenic E. coli and inclusion in routine verification monitoring programs is not recommended. The focus should be on monitoring of control measures for pathogenic E. coli, including prevention of source water contamination by human and animal waste, effective disinfection, and protection of distribution systems from ingress of faecal material. Escherichia coli can be used as a reliable indicator for the presence/absence of pathogenic E. coli.

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NOTE: Important general information is contained in PART II, Chapter 5

References

APHA, AWWA, WEF (American Public Health Association, American Water Works Association, Water Environment Federation) (2005). Standard Methods for the Examination of Water and Wastewater, 21st edition. Method 9260F. Detection of pathogenic bacteria: Pathogenic Escherichia coli. American Public Health Association, Washington DC.

Cameron A, Beers M, Walker C (1995). Community outbreak of hemolytic uremic syndrome attributable to Escherichia coli 0111:NM-South Australia. Morbidity and Mortality Weekly Report, 44:550-558.

Hrudey SE, Hrudey EJ (2004). Safe Drinking Water. Lessons From Recent Outbreaks in Affluent Nations. IWA Publishing, London.

Nataro JP, Kaper JB (1998). Diarrheagenic Escherichia coli. Clinical Microbiology Reviews, 11:142-201.

Rice EW, Johnson CH, Reasoner DJ (1996). Detection of Escherichia coli O157:H7 in water from coliform enrichment cultures. Letters in Applied Microbiology, 23:179-182.

Teunis P, Takumi K, Shinagawa K (2004). Dose response for infection by Escherichia coli O157:H7 from outbreak data. Risk Analysis, 24:401-407.