Did you know that the DNA of microbes can be used to track environmental contaminants much like DNA is used to identify a suspect in a crime? The Forensic Science Program at Marshall University is among a select group of researchers who are tracking fecal pollution to its human and/or animal source. This technique, in general, is known as Bacterial Source Tracking (BST). The MU method for BST uses bacteria (E. coli) uniquely found in human and animal excrement. A fundamental BST assumption is that E. coli, as an intestinal inhabitant of warm-blooded animals and humans, uniquely adapts itself via its genetic material (DNA) in a way that permits the organism to successfully cohabitate with its human or animal host.
Based on this genetic adaptability and variability, microbial DNA “barcodes” can be used to identify the source of fecal pollution. To identify these microbial culprits or “indicators of fecal pollution” in the waterways, the MU BST method requires the development of a database or “library” of known-source fecal isolates (human, cow, horse, chicken, deer, etc.). Through the use of these extensive databases, isolates derived from water samples can be classified by source group (human vs wildlife vs domestic animal). Whether BST is used for surveillance, detection, or post-cleanup assessments, BST can assist water administrators and stakeholders in identifying directed strategies to address the presently spiraling incidence of fecal pollution in our waterways.
Humans, domestic animals and/or wildlife are the primary source of fecal pollution in our waterways. Fecal pollution can enter our waterways in a number of ways including overflow from sewage treatment facilities, “straight-piping”, leaky septic systems in addition to domestic animal and wildlife runoff.
Fecal pollution in the environment has human and animal health implications. Feces is composed of many bacteria, viruses, and other parasitic microorganisms some of which can cause disease and illness.
When released into the environment, these microbes may be ingested, inhaled, or otherwise enter the host through breaks in the skin or mucous membranes to cause illness. After 30 years of the Clean Water Act, many of our nation’s rivers and streams remain “unfishable” and “unswimmable”. One of the primary reasons for this is fecal pollution.
The federal Clean Water Act in 1972 requires all states to monitor waterborne fecal pollution. Under the direction of state Departments of Environmental Protection (DEP) and with the help of other agencies, teams of environmental specialists sample streams and determine their level of fecal impairment – usually described as number of bacteria in 100 milliliter of water.
When repeated measurements demonstrate the bacterial concentration is consistently elevated, a Total Maximum Daily Load (TMDL) is developed. A TMDL is a plan of action used to monitor and clean up streams that are not meeting mandated water quality standards. Once a stream is determined to be impaired, the stream is placed on the 303(d) list for public viewing, and a TMDL is developed for the stream.
While great strides have been made to identify levels or concentration of fecal pollution in our waterways, finding the source or cause of that pollution is necessary if the problem is to be corrected. Finding the source of fecal pollution becomes especially difficult when the contamination is not obvious such as that from non-point sources.
As humans, domestic animals, and wildlife cohabitate many regions of the country, simply reporting high fecal bacterial counts in a waterway does not indicate whether the source is the result of a leaky septic tank, the adjacent feed lot, or the large deer population. In many cases, this distinction and an appropriate plan of action can only be accomplished with Bacterial Source Tracking technology.
With the support of the U.S. Department of Agriculture, a team of specialists at Marshall University is creating BST databases in 5 major watershed regions of West Virginia. A DNA-based BST method is being employed to generate large known-source E. coli libraries that can then be used to estimate the source of waterborne fecal pollution. Studies are currently underway to test the effectiveness of these databases in their region of origin as well as in other regions where local databases currently do not exist.
This DNA-based BST process shows great promise to distinguish between human and non-human fecal contamination and there is every reason to believe we will soon be able to separate the non-human category into domestic and non-domestic animals. In so doing, we have a way to pinpoint the source of fecal contamination and thereby effectively focus remediation efforts in our state and beyond.
With six years of BST experience using the NotI PFGE process, Marshall University is preparing to assist regions and states in adopting this new technology. Activities are currently underway to provide grant and contracted services to federal and state agencies, as well as to private citizens and citizen groups seeking to identify the source of fecal contamination in their region or state.
Forensic Science Center
Forensic Sceince Center
Reprint of Marshall Magazine Spring 2012 Issue used by permission.
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