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 Knowledge for the CommonWealth

Bacterial Source Tracking (BST) Methodology

Crop and Soil Environmental News, July 1999

Charles Hagedorn
Professor and Biotechnology Specialist

BST or Bacterial Source Tracking is new methodology that is being used on fecal bacteria from environmental samples to determine the sources of those bacteria (e.g. from human, livestock, or wildlife origins). BST methodology has been described as having the ability to turn nonpoint sources into point sources. In the scientific literature BST is also called fecal sourcing or fecal typing. BST is new and novel, and must be considered very experimental at present.

Funding for BST research has only become available in the last couple of years. The recent implementation of the total maximum daily loading (TMDL) concept by EPA is the driving force behind BST development. Since the Chesapeake Bay region is being used as one of the national models to implement the TMDL concept, BST has suddenly become very important in Virginia.

Both molecular (genotype) and biochemical (phenotype) BST methods are under development. DNA fingerprinting has received the greatest publicity, but to date there are at least ten or so different methods described in the scientific literature that show potential. However, BST development is so new that no research comparing BST methods or identifying their relative strengths and weaknesses has yet been completed. Such comparison research has only recently been started, and will be conducted over the next few years. It is most reasonable to assume that some combination of BST methods will be needed to provide the most accurate and reliable source identification answers. It is doubtful that any one BST method will emerge as the "best" method for all situations.

Molecular methods offer very precise source identification, but are limited by expense, detailed and time-consuming procedures, and are not yet suitable for assaying large numbers of samples in a reasonable time frame. Biochemical methods may not be as precise, but are simpler, quicker, less costly, and allow large numbers of samples to be assayed in a short period of time. Perhaps the best approach is to use a biochemical method to run large numbers of samples, and then confirm (validate) both the method and the results by assaying some subset of samples by a molecular procedure.

At present, BST can very reliably determine if fecal bacteria are from human or animal sources. If the bacteria are from animal sources, BST can also tell if the animals are livestock or wildlife, but less reliably than the human vs. animal separation. It is unknown at this time if BST can eventually achieve distinctions between different types of livestock or wildlife. Many in the molecular biology community believe such fine differentiations are very feasible.

BST will be heavily used by regulatory agencies in the future. Fecal coliform bacteria are the most widespread problem in Virginia's rivers and streams. Over one-half of the stream segments in Virginia that have been evaluated to date are listed as impaired waters due to fecal coliform populations that exceed water quality standards. The ability to develop realistic total maximum daily loadings (TMDLs) for fecal bacteria, and implementation of cost-effective best management practices (BMPs) for watershed restoration will largely depend on using the new BST methodology to accurately identify sources of fecal pollution in water.

BST methodology is here and it does work, even though it is still considered experimental. Look for BST to be widely used in the near future and to be developed very rapidly.

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