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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #405187
Research Project: Improving Pre-harvest Produce Safety through Reduction of Pathogen Levels in Agricultural Environments and Development and Validation of Farm-Scale Microbial Quality Model for Irrigation Water Sources

Location: Environmental Microbial & Food Safety Laboratory

Title: Spatial variation of tetracycline-resistant E. coli and relationships with water quality variables in irrigation water: A pilot study

Author
item Stocker (ctr), Matthew
item SMITH, JACLYN - Orise Fellow
item Pachepsky, Yakov

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2023
Publication Date: 5/30/2023
Citation: Stocker, M.D., Smith, J., Pachepsky, Y.A. 2023. Spatial variation of tetracycline-resistant E. coli and relationships with water quality variables in irrigation water: A pilot study. Journal of Applied Microbiology. 3(2):504-518. https://doi.org/10.3390/applmicrobiol3020036.
DOI: https://doi.org/10.3390/applmicrobiol3020036

Interpretive Summary: Antibiotic resistant bacteria (ARB) present the major worldwide health concern. ARB can be spread with irrigation water to crops which are later consumed by animals and humans. No science-based sampling protocols are proposed so far for surveying and monitoring ARB in irrigation water sources. Such protocols should account for vARB variation in time and space. In this pilot study, we monitored concentrations of tetracycline-resistant E. coli in a large irrigation pond at 10 locations both at the water surface and at 1-m depth. We discovered that there was a large degree of spatial variation in resistant E. coli and that on some sampling dates, resistance was only detected within samples collected below the pond water surface. We also found that the best indicators of the percentage of resistant E. coli were the concentrations of nitrate and dissolved organic matter. Results of this work can be used by water and health specialists involved in ARB detection, monitoring, prediction, and management in that it demonstrates the need and feasibility for sampling at multiple locations and depths as part of effective sampling strategies to assess the abundance of antibiotic resistant bacteria in surface waters.

Technical Abstract: Irrigation waters may facilitate the spread of antibiotic resistant bacteria or genes to humans and animals. Monitoring of resistance in irrigated waters has become common however many studies do not incorporate a spatial component into sampling designs. The objective of this work was to assess spatiotemporal variations in tetracycline-resistant E. coli in an irrigation pond. Water samples were collected at 10 locations and two different water depths and in situ and laboratory water quality measurements were performed. The percentage of E. coli resistant to the low (4 µg mL-1) and high (16 µg mL-1) tetracycline doses varied by date and location but were observed to be as high as 12.7% and 6.3% of the total population throughout the study, respectively. While significant differences were not observed between resistance levels measured at different depths, on one date resistant E. coli were only detected in samples collected at depth. Nitrate, fluorescent dissolved organic matter, and dissolved oxygen concentrations were found to be the leading control variables for the percentage of resistant E. coli. This work demonstrates that there may be substantial spatial variability in antibiotic resistant E. coli in irrigation ponds which should be accounted for in the design of monitoring programs.