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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Diversity of Escherichia Coli Isolates in Irrigation Water and Associated Sediments: Implications for Source Tracking

Authors
item Lu, Lingeng - TX A&M UNIVERSITY
item Hume, Michael
item Sternes, Keith - SUL ROSS STATE UNIV
item Pillai, Suresh - TX A&M UNIVERSITY

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 11, 2004
Publication Date: September 20, 2004
Citation: Lu, L., Hume, M.E., Sternes, K.L., Pillai, S.D. 2004. Genetic diversity of Escherichia coli isolates in irrigation water and associated sediments: Implications for source tracking. Water Research. 38:3899-3908.

Interpretive Summary: Identifying the sources of fecal bacteria in surface water such as rivers and lakes is of significant importance for environmental quality, food safety and regulatory purposes. Current source tracking approaches rely on the comparison of DNA types among the fecal bacteria. The objective of this study was to compare DNA patterns of E. coli isolated from irrigation water and associated sediments and to evaluate the stability of the E. coli DNA patterns. The isolates were obtained over a 4-month period from specific locations within irrigation canals and sediments associated with the Rio Grande River along the Texas-Mexico border. Different E. coli DNA types were identified among samples collected in each of three locations. Some E. coli obtained over successive months showed consistent DNA patterns, but in the laboratory experiment, the DNA pattern of one E. coli strain changed during survival in irrigation water. These results imply that DNA comparison is of such extreme resolution that it may be a challenging task to rely solely on a DNA comparison-based source tracking DNA fingerprint library for large watersheds.

Technical Abstract: Identifying the sources of fecal contaminants in surface water bodies such as rivers and lakes is of significant importance for environmental quality, food safety and regulatory purposes. Current DNA library-based source tracking approaches rely on the comparison of the genetic relatedness among the fecal contaminants. The objective of this study was to determine the genetic relatedness of E. coli isolated from irrigation water and associated sediments using Pulsed Field Gel Electrophoresis (PFGE) and to evaluate the genetic stability of the E. coli PFGE patterns. The isolates were obtained over a 4-month period from specific locations within irrigation canals and sediments associated with the Rio Grande River along the Texas-Mexico border. Fifty E. coli isolates were genotyped using PFGE. Different E. coli genotypes were identified among samples collected in each of three locations. Some isolates obtained over successive months showed similar genotypic patterns. In the laboratory experiment, the PFGE pattern of one E. coli strain changed during survival in irrigation water. The genetic relatedness of this strain changed from >95% to <83% over 8-week survival. These results imply that PFGE is of such extreme resolution that it may be a challenging task to rely solely on a PFGE-based source tracking DNA fingerprint library for large watersheds.

Last Modified: 11/28/2014
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