71st SWCS International Annual Conference July 24-27, 2016 Louisville, KY

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