Canada Geese

Cattle near stream

Problem

     Fecal contamination of streamwater and groundwater in the Shenandoah Valley poses a significant concern to local water-supply managers.  The complex hydrology of this area and the diverse collection of potential fecal coliform sources make it difficult to link fecal contamination of water systems to the appropriate animal sources.  An emerging technology, bacteria source tracking (BST), can likely identify the sources of fecal contamination in these systems.  Knowledge of the sources of fecal contamination will aid in the development of effective water-protection strategies. Although potentially powerful, bacteria source tracking is relatively new and no consensus is available regarding which method (or combination of methods) is most appropriate for a given situation.

Objective

     This study will compare the ability of seven bacteria source tracking methods to discriminate Escherichia coli isolates from feces of nine different source-animal categories.

Relevance and Benefits

     Information and knowledge gained from this study will advance the field of bacteria source tracking.  The evaluation and comparison of bacteria source tracking methods will provide information that will help investigators across the Nation choose appropriate techniques for determining sources of bacteria in natural waters.

Approach

     The source tracking methods being compared include ribotyping with HindIII; ribotyping with EcoRI and PvuII; antibiotic resistance analysis; pulsed-field gel electrophoresis with Not1; sole source carbon utilization with BIOLOG; rep-PCR with REP primers; and rep-PCR with BOX primers.  These seven methods are being evaluated on their ability to correctly identify 200 blind isolates using a library of 900 known-source isolates.  The known-source library was developed using fecal samples collected from nine sources: humans, dogs, beef cows, dairy cows, swine, chickens, horses, white-tailed deer, and geese.  The collection of blind challenge isolates will test:

·         accuracy with new isolates from the nine sources represented in the known library,

·         precision with replicates from the original known-source library, and

·         robustness with a collection of new sources that are not represented in the known-source 
library (such as mice, cats, goats, and llamas).

Method performance will be assessed by the rate of correct classification of isolates within each source group, the rate of false identification within each source group, and the ability of each method to handle the unrepresented sources.