Bacterial Source Tracking: Potential Application to Drinking Water WellsTerry Gentry1, Maitreyee Mukherjee1, Diane Boellstorff2,

Drew Gholson2, Kevin Wagner3, and George Di Giovanni4

1Texas A&M AgriLife Research; 2Texas A&M AgriLife Extension; 3Texas Water Resources Institute; and 4University of Texas School of Public

Health, Houston, El Paso Branch Campus

Where did the Bacteria (E. coli) Come From?

• Potential sources• Humans• Domesticated animals• Wildlife

• Methods for determining sources• Source survey• Modeling• Bacterial source tracking

What is Bacterial Source Tracking (BST)?

• Used to determine the sources of fecal contamination

• Based on uniqueness of bacteria from individual sources

• A variety of different methods are used

• Often works best as part of a “toolbox approach”

BST Target Organisms• Bacterial v. Microbial Source Tracking• Different targets:

• E. coli• Bacteroidales• Bacteriophage• Human viruses• Chemicals

13 Studies Completed

BST Methods• Library-independent

– Does not require known-source library

– Genotypic detection of microorganisms based on marker genes (DNA)

– Most common markers target Bacteroidales

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What are Bacteroidales?• More abundant in feces than E. coli• Not pathogens• Obligate anaerobes – less likely to

multiply in environment• Subgroups appear to be host

specific• Markers available for humans,

ruminants, horse, hog– Others being tested– Limited wildlife markers

http://www.sourcemolecular.com/newsite/_images/bacteroidetes.jpg

Texas Well Owner NetworkSampling locations

• A total of 159 water samples screened.• Of these, 19 to 58% contained coliform bacteria and 0 to 11% contained E. coli.• Starr county had greatest percentage of wells testing positive for total

coliforms (58%) and tied with Seguin for the highest proportion of wells testing positive for E. coli (11%).

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Navasota New Braunfels Round Rock Seguin Starr County

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Total Coliforms E. coli

Coliform & E. coli Levels

Follow-up Sampling• Eight locations that initially tested positive

for E. coli• Wells varied

- 30 to 350 feet depth- Dug & drilled- Constructed in 1885 to 1984

• Coliforms & E. coli enumerated with IDEXX• Bacteroidales PCR (presence/absence)

- Human (HF183F; Bernard and Field, 2000)- Ruminant (CF128F; Bernard and Field, 2000)- Hog (PF163F; Dick et al., 2005)- Horse (HoF597F; Dick et al., 2005)

Wells Sampled

Sample LocationTotal Coliforms E. coli

----- MPN/100 ml -----1. New Braunfels 55 22. Round Rock >2,420 <13. Starr County 1,203 <14. Starr County 261 385. Starr County >2,420 146. Starr County 649 57. Starr County 1,553 2488. Starr County 30 <1

Coliform & E. coli Levels

Bacteroidales BST Results

BST Summary • Evidence for fecal contamination in all 8 tested

wells• Evidence for ruminant fecal contamination in

63% (5/8) of tested wells• No evidence for human, hog, or horse fecal

sources, but cannot rule these out• Challenges with marker specificity and sensitivity,

especially for private wells• Markers not available for all potential sources

• Continued development and improvement of markers

Questions?Terry GentryTexas A&M University2474 TAMUCollege Station, TX 77843Phone: (979) 845-5323Email: tjgentry@tamu.edu