For detailed information about fecal indicator bacteria and bacteriological water quality visit the U.S.G.S. Water Resource Programs In Michigan.

For background information on E.coli, see "What the heck is an E. coli?"

Magnitude

Despite the fact that elevated levels of fecal coliform bacteria in water are correlated with increased risk of illness, fecal contamination is widespread.

In Minnesota, a 1996 report to Congress stated that 47% of the river miles surveyed could not be used for swimming due to high levels of fecal coliform bacteria. For some rivers the problem is pervasive -- over 90% of the Minnesota River and its tributaries are consistently elevated.

For additional background information see our links and news Web pages.

Problem

Although routine water monitoring is able to determine fecal coliform loads, a simple reliable method to determine the source(s) of contamination is currently unavailable. Possible sources include surface run-off from manure-treated agricultural land or farm animal feedlots, failing or inadequate septic systems, sewer overflow, and wildflife. Source determination is important to develop effective control strategies. Furthermore, the presence of fecal coliform bacteria in high levels may signal the presence of other potential pathogens including Salmonella spp., Shigella spp., hepatitis A virus, and Norwalk group viruses. A method that can discriminate between human and animal fecal sources would provide a tool to improve risk assessments of health effects associated with polluted recreational water.

Possible Source Tracking Tool

The rep-PCR DNA fingerprinting technique is an easy, reliable, and reproducible technique for E. coli source determination. This technique amplifies DNA sequences between repetitive elements in the E. coli genome, and generates a unique pattern of PCR products for each strain. The process is outlined below.

Our complete process can be found on our methods Web page. For more information about other methods of fecal source tracking, such as antibiotic resistance profiles and ribotyping, see our references Web page.

1. Template preparation for PCR reaction and amplification

Whole cells from single colonies are diluted into sterile 1% saline and then boiled for 15 minutes. The extract is then added directly to a PCR master mix containing taq DNA polymerase, BoxA1R primer, and dNTPs. The PCR reactions are placed into thermal cycler to amplify DNA fragments between the repetitive element termed Box.

2. Electrophoresis, pattern analysis and classification

The amplified fragments are resolved in a gel matrix to yield a genomic fingerprinting profile (similar to "bar codes" in a supermarket). The gels are photographed and the digital images are saved. The fingerprints are then analyzed by pattern recognition computer software. A database, consisting of E. coli fingerprints from known human and animal sources was constructed.

Implications

The ability to distinguish the sources of fecal contamination is an important assessment tool, both for assessment of possible health risks and to facilitate effective clean-up strategies. From a public health perspective, contamination from human sources poses a greater human health risk than that originating from animal sources. Armed with knowledge about the sources of pollution, agencies could respond rapidly and develop more tailored and cost effective abatement efforts.