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Antimicrobial resistance in escherichia coli and enterococcal isolates from irrigation return flows in a high-desert watershed

Dungan, R.S. and Bjorneberg, D.L. (2021) Antimicrobial resistance in escherichia coli and enterococcal isolates from irrigation return flows in a high-desert watershed. Frontiers in Microbiology. 12. 12 May 2021. Available: Https://

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Irrigation return flows (IRFs) are of interest because they collect surface runoff and subsurface drainage, causing them to have elevated contaminant and bacterial levels, and making them a potential point source of pollutants. The purpose of this study was to determine antibiotic susceptibility profiles of E. coli and Enterococcus spp. that were collected from IRFs in south-central Idaho. Environmental isolates can be a potentially important source of antibiotic resistance (AR) and IRFs may be one way resistance genes are transported out of agroecosystems. Water samples were collected from nine IRFs and one background site (canal water from Snake River) on a biweekly basis during 2018. Escherichia coli and Enterococcus were enumerated via a Most Probable Number technique, then subsamples were plated on selective media to obtain isolates. About 185 of 800 unique isolates for E. coli and Enterococcus were tested for antimicrobial susceptibility using the Sensititre broth microdilution plates. For E. coli, 11% of the isolates were resistant to tetracycline, with fewer numbers being resistant to the 13 other antibiotics, with none resistant to gentamicin. While 77% of the E. coli isolates were pan-susceptible, 9 MDR patterns with resistance up to 7 drug classes (10 antibiotics) occurred in 11 isolates. For the enterococcal species, only 9% of isolates were pan-susceptible and the single highest resistance was to lincomycin (75%) followed by nitrofurantoin (31%) and tetracycline (11%). In addition, 13 enterococcal isolates were determined to be MDR to up to 5 different drug classes and it was only prevalent among E. faecalis, E. faecium, E. casseliflavus, and E. thailandicus. Due to the potential for human contact, routine monitoring of E. coli and Enterococcus in the IRFs could be a useful tool to understand the long-term trends of AR in this mixed-use watershed.

Item Type: Article
NWISRL Publication Number: 1703
Subjects: Water > Water management
Water > Water quality
Depositing User: Users 6 not found.
Date Deposited: 13 May 2021 18:30
Last Modified: 13 May 2021 18:30
Item ID: 1741