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Title: Genetic diversity and antimicrobial resistance of Escherichia coli from human and animal sources uncovers multiple resistances from human sources

Author
item Ibekwe, Abasiofiok - Mark
item MURINDA, SHELTON - California Polytechnic State University
item GRAVES, ALEXANDRIA - North Carolina State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2011
Publication Date: 6/8/2011
Citation: Ibekwe, A.M., Murinda, S.E., Graves, A.K. 2011. Genetic diversity and antimicrobial resistance of Escherichia coli from human and animal sources uncovers multiple resistances from human sources. PLoS One. 6(6):1-12.

Interpretive Summary: Escherichia coli (E. coli) are widely used as indicators of fecal contamination of waterways in most urban areas throughout the United States. It is naturally present in the intestinal tracts of warm-blooded animals, and is released into the environment through deposition of fecal material. In many watersheds, sources of E. coli may be from human, farm animals, wildlife, and pets, etc. The goals of this study were to determine the distribution of E. coli as it relates to sources that may affect water quality within the Santa Ana River watershed and to characterize E. coli from surface water and sediment samples based on their genetic profiles and their resistances to some antibiotics. There were no differences in E. coli populations between Chino creek (urban runoff sources) and Cypress channel (agricultural sources); however, E. coli genotypes determined by pulse field gel electrophoresis (PFGE) were less diverse in Cypress channel than in Chino creek. In addition, more isolates originating from urban runoff sources than agricultural sources carried multiple resistances to more than one antibiotic. The use of different kinds of antibiotics for different therapeutic end points, and other commercial products in urban environment may contribute to the development of antibiotic resistant bacteria in the environment. The acquisition of antibiotic resistance in bacteria may be the first indicator of the impact of the emerging pollutants on the environment, which may be linked directly to the pollutant sources. The results of this research will be used by water quality managers from different water districts, researchers, and EPA for Total Daily Maximum Daily Load assessments for large and mixed watersheds.

Technical Abstract: Escherichia coli are widely used as indicators of fecal contamination, and in some cases to identify host sources of fecal contamination in surface water. Prevalence, genetic diversity and antimicrobial susceptibility were determined for 600 generic E. coli isolates obtained from surface water and sediment from creeks and channels along the middle Santa Ana River (MSAR) watershed of southern California, USA, after a 12 month study. Evaluation of E. coli populations along the creeks and channels showed that E. coli were more prevalent in sediment compared to surface water. E. coli populations were not significantly different (P = 0.05) between urban runoff sources and agricultural sources, however, E. coli genotypes determined by pulsed-field gel electrophoresis (PFGE) were less diverse in the agricultural sources than in urban runoff sources. PFGE also showed that E. coli populations in surface water were more diverse than in the sediment, suggesting isolates in sediment may be dominated by clonal populations. Twenty four percent (144 isolates) of the 600 isolates exhibited resistance to more than one antimicrobial agent. Most multiple resistances were associated with inputs from urban runoff and involved the antimicrobials rifampicin, tetracycline, and erythromycin. The occurrence of a greater number of E. coli with multiple antibiotic resistances from urban runoff sources than agricultural sources in this watershed provides useful evidence in planning strategies for water quality management and public health protection.