Microbial contamination generally comes from untreated human or animal fecal wastes that enter the watershed from specific point sources, or more commonly from non-point sources. E. coli bacteria have been used as an indicator of fecal contamination for many years. E. coli is a subgroup of the fecal coliform bacteria, which are themselves a subgroup of the total coliform bacteria. E. coli tend to be the most feces specific of these three groups and are characterized by their ability to propagate at elevated temperatures, similar to the temperatures found in the mammalian gastrointestinal tract.
An ideal indicator has many characteristics, one of which is that they are present when pathogenic organisms are present and not if pathogens are not present. In the case of E. coli, in some environments, this has tended to be a problem due to their instability in relation to pathogens of concern. One such environment is estuarine and marine water, where there is elevated salinity. Because of this, the enterococci, a more fecal-specific subgroup of the fecal streptococci, have been proposed and used in these environments.
However, none of these bacterial indicators tend to be good indicators of viral and parasitic pathogens. Researchers have proposed and used male-specific coliphages, viruses that infected E. coli bacteria, as indicators of viral contamination in environmental waters with great success. To date, appropriate parasite indicators have not been identified; however, many people suggest the use of certain bacterial spores (i.e., Cl. perfringens and Bacillus) for this purpose. The bacterial spores are similar in morphology and other characteristics as the environmentally stable cysts and oocysts of the parasites.
Furthermore, to determine watershed contaminants, it is important to use source-tracking tools (see Question V-1). These source-tracking tools can be used to determine source attribution for microbial contaminants in a watershed and include ribotyping for bacteria, antibiotic resistance patterning for bacteria, and typing methods for male-specific coliphages. Many of these techniques are expensive and time-consuming and cannot be implemented on a routine basis by many water quality laboratories.
To conclude, E. coli may be the better indicator organism to measure if time and resources dictate measurement of only a single indicator; however, the more prudent approach would be to measure a suite of microbial indicators that would be representative of each of the major classes of pathogens. Once isolated, and given the proper resources, the isolated microbial indicators can be further characterized to potentially determine the source of the microbial contamination.
Additional Reading
Hagedorn C., S.L. Robinson, J.R. Filtz, S.M. Grubbs, T.A. Angier, and R.B. Reneau Jr. 1999. Determining Sources of Fecal Pollution in a Rural Virginia Watershed with Antibiotic Resistance Patterns in Fecal Streptococci. Applied and Environmental Microbiology 65(12):5522–5531.
Jamieson, R.C., R.J. Gordon, S.C. Tattrie, and G.W. Stratton. 2003. Sources and Persistence of Fecal Coliform Bacteria in a Rural Watershed. Water Quality Research Journal of Canada 38(1):33–47.
Scott, T.M., J.B. Rose, T.M. Jenkins, S.R. Farrah, and J. Lukasik. 2002. Microbial Source Tracking: Current Methodology and Future Directions. Applied and Environmental Microbiology 68(12):5796–5803.
Stewart-Pullaro, J., J.W. Daugomah, D.E. Chestnut, D.A. Graves, M.D. Sobsey, and G.I. Scott. 2006. F+RNA Coliphage Typing for Microbial Source Tracking in Surface Waters. Journal of Applied Microbiology (in press).
Thurston-Enriquez, J.A., J.E. Gilley, and B. Eghball. 2005. Microbial Quality of Runoff Following Land Application of Cattle Manure and Swine Slurry. Journal of Water and Health 3(2):157–171.
