Author of Response: Chip Simmons, PhD, Assistant Research Professor at the University of North Carolina-Chapel Hill, School of Public Health, osimmons@email.unc.edu

Response: Wells are not generally tested for microbial pathogens because pathogen testing is time consuming, very expensive, and often technically difficult. Additionally, many times it is hard to know which specific pathogen or even which class of pathogen to test for without there being clinical infections.

In contrast to testing for pathogens, most water quality experts test for microbial indicator organisms that are representative of fecal contamination. The most common fecal indicators are the total coliform bacteria, fecal (thermotolerant) coliform bacteria, and E. coli. Total coliform bacteria are many times not feces specific but do provide the most conservative measure of water quality. Fecal (thermotolerant) coliform bacteria are a subset of the total coliform bacteria that can grow at elevated temperature (44.5°C); these tend to be more feces specific because they grow only at elevated temperatures similar to that found in warm-blooded mammals. E. coli are a specific subset of the fecal coliform bacteria, tend to be very feces specific, and are the most indicative of fecal contamination of water. However, there are sometimes problems with these bacterial indicators because they may be more easily inactivated in the environment than the pathogens of concern. Because of this, another group of fecal bacteria, the enterococci spp. have been suggested for use in some cases, most specifically for measuring the quality of estuarine and marine waters for bathing water quality. All of these bacterial indicator organisms are generally robust indicators for bacterial pathogens.

However, there have been many documented cases of waterborne viral outbreaks of gastroenteritis associated with water that meet the bacterial indicator standards. Because of this, male-specific coliphages, viruses that infect certain bacteria, have proven to be better indicators of viral contamination of waters. The coliphages tend to be more indicative of enteric viruses infecting humans and animals because they are viruses similar in size, structure, and properties to the pathogenic enteric viruses of concern.

In summary, microbial indicators are tools used for measuring the microbiological quality of water, and it is most prudent to use a suite of indicator organisms that will be indicative of different classes of pathogens.

Additional Reading:
Anderson, M., and M.D. Sobsey. 2006. Detection and Occurrence of Antimicrobially Resistant Enteric Bacteria On or Near Swine Farms in Eastern North Carolina. Water Science and Technology. Vol. 54(3):211–218.

Bitton, G., S.R. Farrah, R.H. Ruskin, J. Butner, and Y.J. Chou. 1983. Survival of Pathogenic and Indicator Organisms in Ground Water. Ground Water. Vol. 21(4):405–410.

Conboy, M.J., and M.J. Goss. 2001. Identification of an Assemblage of Indicator Organisms to Assess Timing and Source of Bacterial Contamination in Groundwater. Water, Air, & Soil Pollution. Vol. 129:101-118.

Crane, S.R. and J.A. Moore. 1984. Bacterial Pollution of Groundwater: A Review. Water, Air, & Soil Pollution. Vol. 22(1):67-83.