Contaminant of the Month: E. coli and other fecal bacteria in drinking water

May 1, 2015

E. coli detections in food and water are a good indication that relatively recent sewage/sanitary contamination has occurred.

What they are:

  • Coliforms (total coliforms) are diverse bacteria that live (not exclusively) in the intestines of warm-blooded animals.
  • Thermotolerant fecal coliforms are a subgroup that can ferment lactose at 44o to 45o C (111.2o to 113o F).
  • E. coli (Escherichia coli) are a subgroup of fecal coliforms. They are gram-negative, rod-shaped bacteria named after Theodor Escherich, who discovered them in 1885.
  • There are numerous species and strains of each and most are not harmful, but some can infect humans.
  • E. coli constitute about 0.1 percent of gut flora, so they are present in greater numbers than pathogens and are usually beneficial.
  • E. coli are the most important indicator bacteria for relatively recent fecal contamination, because they are more numerous than fecal pathogens, can survive in the environment and are similarly subject to water treatment.
  • Risks are associated with exposures to sewage/sanitary contaminated milk and food, recreational water and drinking water.
  • Apart from the disease concerns of some strains, E. coli have many uses in biotechnology, including recombinant DNA research.

Health effects:

  • Nonpathogenic E. coli begin to colonize an infant’s GI tract (gastrointestinal tract) within 40 hours after birth from food, water or human contact.
  • E. coli detections in food and water are a good indication that relatively recent (perhaps 10 to 15 days) sewage/sanitary contamination has occurred. They survive longer at lower temperatures.
  • They reproduce rapidly under ideal conditions, doubling in 20 minutes.
  • They are good indicators for potential bacterial and viral contamination in water.
  • Certain pathogenic strains can cause diarrhea and illnesses such as gastroenteritis, urinary tract infections, neonatal meningitis, hemolytic-uremic syndrome, peritonitis, septicemia and some pneumonia.
  • Shiga toxin-producing strains such as E. coli 0157:H7 cause hemolytic-uremic syndrome, which has many serious health outcomes and often death.

Water treatment:

  • E. coli are effective treatment indicators for bacteria and viruses but not protozoa.
  • Standard disinfection with chlorine, hypochlorite, chlorine dioxide, ozone and ultraviolet (UV) are effective in minutes in low turbidity water, as well as chloramines with much longer concentration x time values.
  • Protozoa are not as susceptible to disinfection as are E. coli and bacterial and viral pathogens, thus filtration is necessary for removal, although UV is also effective; boiling will eliminate all pathogens.
  • POU carbon filters do not remove pathogens. If they contain silver, it is only to reduce microbial regrowth on the filter and not to disinfect the water.
  • POU is not permitted for meeting microbial drinking water standards in public water supplies.
  • Appropriate POE systems can be used for decentralized compliance.


  • Optimal growth of E. coli occurs at 37o C (98.6o F), which is normal body temperature.
  • Traditional analyses involve membrane filtered culture plating in a microbiology laboratory.
  • In recent years, Colilert®-type methods involving production of the enzyme ß-glucuronidase have greatly simplified the analyses for E. coli. The enzyme produced by E. coli partially metabolizes a marker chemical that then produces color.
  • Kits costing about five dollars per test allow testing under nonmicrobiology laboratory conditions.
  • The water sample with the reagent is retained for 18 to 24 hours at approximately 98o F (36.67o C). As a presence/absence test, appearance of a yellow color indicates total coliforms; fluorescence under a UV lamp indicates E. coli.
  • Quantification can be done using multiple dilutions.


  • Disinfection and filtration drinking water regulations have reduced risks of waterborne diseases.
  • The current drinking water regulations have an MCL of < 1/100 ml only for E. coli or fecal coliforms.
  • Analyses for total coliforms are still required, but they are used primarily to indicate whether there are sanitary flaws in the system that should be corrected.
  • If E. coli are verified and not corrected immediately, there is the potential for a boil water notice to be issued because of the connection with sewage contamination.

Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.

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