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FECAL SOURCE TRACKING BY ANTIBIOTIC RESISTANCE ANALYSIS ON A RURAL WATERSHED
OLIVAS, Y. AND B. R. FAULKNER. FECAL SOURCE TRACKING BY ANTIBIOTIC RESISTANCE ANALYSIS ON A RURAL WATERSHED. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, 139(1-3):15-25, (2008).
The Turkey Creek watershed located in northwestern Oklahoma, sustains approximately 40000 head of livestock. In addition, the stream receives partially-treated municipal waste from various towns. E. coli was enumerated quarterly and counts beyond EPA limit were found in spring and summer. These counts correlated with higher ambient temperature and precipitation. Microbial source tracking by antibiotic resistance analysis (ARA) was performed, and this method was challenged with the use of long-term frozen Escherichia coli (E. coli). The resistance patterns of 772 water-isolates and a source-library containing 2250 isolates were developed testing with nine antibiotics. Low antibiotic resistance was frequently observed among sources, therefore, antibiotic concentrations and scoring were adjusted to obtain measurable resistance. In that respect sensible flexibility was observed. Seasonal discriminant analysis (DA) of stream E. coli isolates indicated that in spring (43%), and summer (37%), human contributions were not significantly higher than the respective livestock contributions of 40% and 35% (P = 0.66 and 0.77 by an odds ratio test). However, the misclassification rates into the human source were high (17%) and the average rate of correct classification (ARCC) was 65%. Therefore, the classification was revised using the rates of misclassification. After revision, livestock scored 53% in spring and 48% in summer (P = 0.07, and 0.06 respectively). Annual DA of stream isolates assigned 43%, 35%, and 22% to human, livestock, and deer respectively. After revision, the classification became human 36%, livestock 48%, and deer 16%. The differences between the original and revised classification (P = 0.31, 0.06, and 0.28) showed that livestock scored higher, and defined as the leading source of the fecal pollution. Based on the ARCC and MST results, the performance of ARA with long-term frozen E.coli was found acceptable.
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Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
GROUND WATER AND ECOSYSTEMS RESTORATION DIVISION
ECOSYSTEM & SUBSURFACE PROTECTION BRANCH