This document discusses bacterial source tracking (BST) as a potential tool to identify the source of fecal contamination in drinking water wells. It provides an overview of BST methods, which use genetic markers to detect the presence of specific types of bacteria that indicate contamination from humans, livestock, wildlife or other sources. The document describes a study that used BST to analyze samples from 8 wells in Texas that previously tested positive for E.coli. The results found evidence of ruminant (cow/goat/sheep) fecal contamination in 5 of the 8 wells, but no conclusive evidence of human, hog, or horse sources. The study highlights both the promise and challenges of BST for identifying sources of well contamination.

1. Bacterial Source Tracking: Potential
Application to Drinking Water Wells
Terry 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

2. Where did the Bacteria (E. coli) Come From?
• Potential sources
• Humans
• Domesticated animals
• Wildlife
• Methods for determining sources
• Source survey
• Modeling
• Bacterial source tracking

3. 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”

4. BST Target Organisms
• Bacterial v. Microbial Source Tracking
• Different targets:
• E. coli
• Bacteroidales
• Bacteriophage
• Human viruses
• Chemicals

5. 13 Studies
Completed

6. BST Methods
• Library-independent
– Does not require known-source
library
– Genotypic detection of
microorganisms based on marker
genes (DNA)
– Most common markers target
Bacteroidales
+ + +- +- -
M 1 2 3 4 5 6 7

7. 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/new
site/_images/bacteroidetes.jpg

8. Texas Well Owner Network
Sampling locations

9. • 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%).
19
43
47
32
58
0
4 5
11 11
0
10
20
30
40
50
60
70
Navasota New Braunfels Round Rock Seguin Starr County
PositiveSamples(%)
Total Coliforms E. coli
Coliform & E. coli Levels

10. 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)

11. Wells Sampled

12. Sample Location
Total Coliforms E. coli
----- MPN/100 ml -----
1. New Braunfels 55 2
2. Round Rock >2,420 <1
3. Starr County 1,203 <1
4. Starr County 261 38
5. Starr County >2,420 14
6. Starr County 649 5
7. Starr County 1,553 248
8. Starr County 30 <1
Coliform & E. coli Levels

13. Bacteroidales BST Results

14. 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

15. Questions?
Terry Gentry
Texas A&M University
2474 TAMU
College Station, TX 77843
Phone: (979) 845-5323
Email: tjgentry@tamu.edu