E. coli: Indicator of Fecal Pollution and Human Health Risk

Escherichia coli (E. coli), a bacteria found in the gut of warm blooded animals, is the USEPA recommended indicator of fecal contamination in fresh waters. It is present in high numbers in the gastrointestinal tracts of vertebrate animals and therefore provides a senstive measure of fecal pollution.

The USEPA recommended limit of E. coli is 235 CFU ("Colony Forming Units" or cells) per 100 mL for recreational waters. Disease-causing organisms can be carried in fecal-contamination, and the detection of high levels of E. coli indicates that pathogens such as enteroviruses, Norwalk viruses, Coxsakie A and B, Hepatitis A, Shigella spp., and Salmonella spp. may be present.

Typical testing for E.  coli cannot not differentiate the source of the contamination(e.g. animal vs. human), since it is present in all warm-blooded mammals.

 

Picture: E. coli and other fecal coliforms growing on nutrient-rich mTEC agar at 44.5oC

Sources of E. coli in Surface Waters

Despite efforts to improve sewer infrastructure and agricultural management practices, poor water quality persists in Lake Michigan, particularly in large urban areas such as Milwaukee. Agricultural runoff, urban stormwater and sewage overflows are all potential sources of contamination in waterways. Detecting contamination is relatively simple compared to the challenge of identifying where such contamination may originate. Fecal coliforms and E. coli are bacteria commonly used in water quality testing to detect fecal pollution. These organisms are present in high numbers in the gastrointestinal tract of almost all warm-blooded animals, and are therefore easy to detect in feces-contaminated water. Fecal coliforms and E. coli generally do not pose the actual health risk, but rather demonstrate the presence of fecal matter, which may carry numerous pathogenic (disease causing) organisms. The USEPA has determined that if levels of E. coli exceed 235 organisms (Colony Forming Unit or CFU) per 100 mL of water, a health risk to humans may exist and an recreational water quality advisory should be issued.

Sewage Overflows

Human fecal pollution in urban areas is largely attributed to sewage overflows.  There are two types of sewage overflows; sanitary sewer overflows (SSOs), and combined sewer overflows (CSOs).  SSOs are the release of untreated sewage from municipal sanitary sewers directly into surface water bodies.  There are numerous causes of SSOs including extreme weather, system failure, incorrect system operation and maintenance, and vandalism.  Combined sewer systems carry both sanitary sewage and stormwater to a treatment plant.  During wet-weather periods these combined systems may exceed their holding capacity due to the increased amount of stormwater entering the system, and, as a result, this combined sewage is discharged directly into the nearby surface waters.  E. coli levels in sewage discharge have been found to reach 500,000 CFU/ 100 mL for an SSO, and 250,000 CFU/ 100 mL from a CSO.

Stormwater Runoff

Stormwater is a major contributor of bacterial and chemical non-point source pollution in watersheds.  Urban and suburban areas generate higher volumes and more highly polluted stormwater runoff than land covered in natural vegetation due to the amount of pavement and rooftops (impervious surfaces) in developed areas. E. coli levels in urban stormwater can reach as high as 100,000 CFU/ 100 mL.

 

Agricultural Runoff

Fecal contamination from agricultural animal runoff poses an additional threat to water quality. E. coli levels from feedlot runoff typically ranges between 10,000 to 100,000 CFU/ 100mL and is accompanied by nutrient and sediment contaminants.

 

 

Wildlife

Localized inputs of fecal bacteria from wildlife, such as waterfowl roosting on shorelines, can negatively impact water quality.  According to a study conducted by our laboratory at a Milwaukee beach on Lake Michigan, E. coli levels reaching over 27,000 CFU/ 100 mL were